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So my commutes are all relatively short. Less than 10 miles. But I decided to go across town and do some country road business. What’s differential whine sound like? Cause after a while I thought I heard a type of whine coming from the rear of the car.
 

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The diff whine is kind of a high pitch gear whine (seems like it is coming from the back but hard to pinpoint its exact location) and usually occurs around +40mph. The pitch changes with speed and tends to show up when the diff oil is warmed up and you maintain a slight torsional load on the drivetrain. Usually accelerating or decelerating at highway speeds increases its presence.

I have tried different oil brands and weights (although never tried the non-newtonian Lucas gear lube) and for me it never went away. Plenty of guys around here have the problem and it does not seem to be a big mechanical issue but it is a big nuisance, like a mosquito buzzing past your ear...constantly. Most just crank up the radio. Some have replaced the diff (more cost effective than trying to attempt to shim the pinion bearing) only for the whine to reappear, usually after a nasty wheel hop.
 

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Join the club buddy. Mine is new too (7k miles), and I have it as well, specifically over 80mph. I plan on having dealer replace fluid, replace differential, or replace the driveshaft. I've read forum posts here and elsewhere that lead me to believe it could be either the driveshaft or diff that are causing issue. Some report replacing them fixes it, others don't. It's annoying.

I keep trying to fix it by doing 90 degree burnouts around corners. No dice yet.
 

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So my commutes are all relatively short. Less than 10 miles. But I decided to go across town and do some country road business. What’s differential whine sound like? Cause after a while I thought I heard a type of whine coming from the rear of the car.
My Hellcat manifests some kind of differential whine. ChallyTatum describes it as good as I could.

At one point when I had the car out and had the opportunity to obtain some speeds that I had not been able to obtain before the noise was rather unhealthy sounding.

But at slower speeds the noise was not real bad. I sort of treat it like the supercharger whine. Just part of the car's aural experience.

The whine was getting a bit worse but the change appeared to be slight.

But then it got lots better when a while back due to a rear tire puncture I had to replace both rear tires even though they had some life left. They were worn -- oh this at 13799 miles -- just looked it up on the service invoice -- but had at least another 13/14K miles left of service life.

After the new rear tires were fitted the "whine" was diminished and especially at the higher speeds. I believe part of my Hellcat's differential whine is just tire noise that gets worse as the tires wear. The tire wear does not suggest any alignment issues, the tire wear front and back and side to side is very even. At 10K miles the dealer rotated the tires but the service invoice had the tread depths for all 4 tires noted and all were the same.

Next service will be at 20K miles and at this time I'll book the car in for not only oil/filter but for a diff fluid service.

Right now the fluid service is just my usual desire to have one done early not because I think the diff's wonky.
 

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I agree Chally Tatum described the whine very well. The only thing I can add is the whine is most noticeable at relatively low speed when backing off the throttle just enough to unload the drivetrain or applying very light throttle, just enough to lightly load the drive train.

I changed the diff fluid to Royal Purple 75W-140 about 500 miles back. At first there was no difference in the whine but now it sounds like it slightly reduced. Can't hear it under most driving situations but can still hear it under situation I described above although it is slightly softer.
 

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This is from West Coast Differentials on noisy rear gear/axle noises.
  • Whirring noise only while decelerating at any or all speeds is most likely caused by bad pinion bearings or loose pinion bearing preload, and almost never by bad ring and pinion gears.
  • A howl or whine during acceleration over a small or large speed range is usually caused by worn ring and pinion gears or improper gear set up.
  • Rumbling or whirring at speeds over about 20 mph can be caused by worn carrier bearings. The noise may change while turning.
  • Regular clunking every few feet may indicate broken ring or pinion gears.
  • Banging or clunking only on corners can be caused by broken spider gears, lack of sufficient positraction lubrication, or worn positraction clutches.
  • Rumble while turning may indicate bad wheel bearings.
  • A steady vibration that increases with the vehicle’s speed can be caused by worn u-joints or an out of balance driveshaft.
  • Clunking only when starting to move or getting on and off the gas might be loose yokes, bad u-joints or worn transfer case or transmission parts
 

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Rob446 did you notice a difference in MPG with the high viscosity diff oil? Maybe it is all in my head but I swore I lost almost 1MPG. Again probably in my head.
 

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This is from West Coast Differentials on noisy rear gear/axle noises.
  • Whirring noise only while decelerating at any or all speeds is most likely caused by bad pinion bearings or loose pinion bearing preload, and almost never by bad ring and pinion gears.
  • A howl or whine during acceleration over a small or large speed range is usually caused by worn ring and pinion gears or improper gear set up.
  • Rumbling or whirring at speeds over about 20 mph can be caused by worn carrier bearings. The noise may change while turning.
  • Regular clunking every few feet may indicate broken ring or pinion gears.
  • Banging or clunking only on corners can be caused by broken spider gears, lack of sufficient positraction lubrication, or worn positraction clutches.
  • Rumble while turning may indicate bad wheel bearings.
  • A steady vibration that increases with the vehicle’s speed can be caused by worn u-joints or an out of balance driveshaft.
  • Clunking only when starting to move or getting on and off the gas might be loose yokes, bad u-joints or worn transfer case or transmission parts
#2 is what best describes the conditions when I hear whine but I also hear it during decel, although when I push in the clutch it is pretty much gone. Seems to only occur when the drive line has some torsion on it.
 

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It also seems to be more of a thing with manual trans challengers. I wonder if the charger guys complain about a rear diff whine?
 

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I'm sure the direct connection between rear dif, driveshaft, and trans will magnify noises. The 2 piece drive shaft is there to minimize vibration noise I've heard. Why these weren't built with actual u-joints, solid drive shaft is beyond my thinking, but maybe it's the way it is to make it quieter for the great American public. Why hasn't somebody come out with bolt in cradle conversion coil over 4 link solid axle system yet??? A Curry 9" solid axle would make the rear end bulletproof to me. IDK................
 

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My auto SRT has a whine at part throttle (almost coasting) but is quiet otherwise, as long as it is not causing wear or other damage I am happy to live with it...
I am saying this after reading all of the posts of having them fixed only for the annoying noise to reappear, I am not prepared to go to all of that effort only to end up where I started.
 

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I will try to calm your nerves a bit here. The noise appears during a certain speed range, typically around 50-60 MPH and will instantly go away when you remove load from the drive train. I also have a 6speed manual in my car.

This condition has been with my car since new, which was November of 2014 when the scat packs first started to arrive on dealer lots. 20k miles and 5 years later, the sound is no better or worse. Even though there is a service bulletin on this condition, I've chosen not to have the rear replaced. The reason that I made this choice is because two other local owners who had this harmonic nuisance went ahead with the warranty repair. One guy has the noise only it's worse now than the original rear. The other guy had about two weeks of no noise and then it came right back just the same.
 

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Rob446 did you notice a difference in MPG with the high viscosity diff oil? Maybe it is all in my head but I swore I lost almost 1MPG. Again probably in my head.
I don't monitor MPG closely enough to give you an accurate answer. I decided to use 75W-140 after changing diff fluid in my Ram, it made a very noticeable difference in the sound and feel of the truck. Had the better part of a quart remaining so decided to use the heavier fluid in the Challenger with the idea I may switch to 75W-90 after running 75W-140 for a while.

I complained about the noise to the dealer. The said they were unable to hear the noise but scoped the diff and said they could not find any wear or heat marks and the fluid looked perfect. The service bulletin related to rear end noise specified a check that identified noises while executing turns. My car did not exhibit the symptoms discussed in the service bulletin.
 

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My DIFF (or rear end) noise is present while driving, but its very quiet. I only really hear it EXACTLY after 80MPH. Before 80MPH its super hard to even notice it.
 

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This is from West Coast Differentials on noisy rear gear/axle noises.
  • Whirring noise only while decelerating at any or all speeds is most likely caused by bad pinion bearings or loose pinion bearing preload, and almost never by bad ring and pinion gears.
  • A howl or whine during acceleration over a small or large speed range is usually caused by worn ring and pinion gears or improper gear set up.
  • Rumbling or whirring at speeds over about 20 mph can be caused by worn carrier bearings. The noise may change while turning.
  • Regular clunking every few feet may indicate broken ring or pinion gears.
  • Banging or clunking only on corners can be caused by broken spider gears, lack of sufficient positraction lubrication, or worn positraction clutches.
  • Rumble while turning may indicate bad wheel bearings.
  • A steady vibration that increases with the vehicle’s speed can be caused by worn u-joints or an out of balance driveshaft.
  • Clunking only when starting to move or getting on and off the gas might be loose yokes, bad u-joints or worn transfer case or transmission parts
Thanks for this man. Good info.
 

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FYI - the FSM has some additional info but not as concisely written as WCD.


GEAR NOISE

Axle gear noise can be caused by insufficient lubricant, incorrect backlash, incorrect pinion depth, tooth contact, worn/damaged gears, or the carrier housing not having the proper offset and squareness.

Gear noise usually happens at a specific speed range. The noise can also occur during a specific type of driving condition. These conditions are acceleration, deceleration, coast, or constant load.

When road testing, first warm-up the axle fluid by driving the vehicle at least 5 miles and then accelerate the vehicle to the speed range where the noise is the greatest. Shift out-of-gear and coast through the peak-noise range. If the noise stops or changes greatly:

  • Check for insufficient lubricant.
Differential side gears and pinions can be checked by turning the vehicle. They usually do not cause noise during straight-ahead driving when the gears are unloaded. The side gears are loaded during vehicle turns. A worn pinion shaft can also cause a snapping or a knocking noise.

BEARING NOISE

The differential and pinion bearings can produce noise when worn or damaged. Bearing noise can be either a whining, or a growling sound.

Pinion bearings have a constant-pitch noise. This noise changes only with vehicle speed. Pinion bearing noise will be higher pitched because it rotates at a faster rate.

Worn or damaged differential bearings usually produce a low pitch noise. Differential bearing noise is similar to pinion bearing noise. The pitch of differential bearing noise is also constant and varies only with vehicle speed.

Wheel hub bearings produce noise and vibration when worn or damaged. The noise generally changes when the bearings are loaded. Road test the vehicle. Turn the vehicle sharply to the left and to the right. This will load the bearings and change the noise level. Where axle bearing damage is slight, the noise is usually not noticeable at speeds above 30 mph.

LOW SPEED KNOCK

Low speed knock is generally caused by a worn joint or by worn side-gear thrust washers. A worn pinion shaft bore will also cause low speed knock.

VIBRATION

Vibration at the rear of the vehicle is usually caused by a:

  • Damaged propeller shaft.
  • Missing propeller shaft balance weight(s).
  • Worn or out-of-balance wheels.
  • Loose wheel lug nuts.
  • Worn Constant Velocity (CV) joints.
  • Loose/broken springs.
  • Loose pinion gear nut.
  • Excessive pinion CV flange run out.
  • Bent halfshaft(s).
Check for loose or damaged front-end components or engine/transmission mounts. These components can contribute to what appears to be a rear end vibration. Do not overlook engine accessories, brackets and drive belts.

All driveline components should be examined before starting any repair.

DRIVELINE SNAP

A snap or clunk noise when the vehicle is shifted into gear, can be caused by:

  • High engine idle speed.
  • Transmission shift operation.
  • Loose engine/transmission/transfer case mounts.
  • Worn Constant Velocity (CV) joints.
  • Worn or broken axle mount isolators.
  • Loose pinion gear nut and CV flange.
  • Excessive ring gear backlash.
  • Excessive side gear to case clearance.
The source of a snap or a clunk noise can be determined with the assistance of a helper. Raise the vehicle on a hoist with the wheels free to rotate. Instruct the helper to shift the transmission into gear. Listen for the noise, a mechanics stethoscope is helpful in isolating the source of a noise.
 

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Since these cars have IRS and the diff is actually mounted to the chassis through rubber isolators instead of being suspended by springs on the ends, any noise is more likely to be transmitted to the driver's compartment.

Noises you would never hear on a car with a live rear axle will show up.

If there is no metal in the diff fluid and nothing is clunking or broken, it's just an annoyance. I did seem to notice it more once I installed my diff brace, which makes sense since it is another connection point for transmission of sound vibrations.
 

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So my 5.7 JGC also has IRS and a 230mm diff (yes it has more sound deadening material but in the cargo area it is just carpet) and not a whine, whimper or peep.
 

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Lots of good information and as most said, not much to do about it. Both of my SRTs had the same noise at around 50-60, depending on throttle input. Sometimes louder when coasting down a hill, sometimes when on the gas. With windows down, don't hear anything. Only when they are up do I hear it, but doesn't bother me. I've had worse rear whines, just about every V8 RWD car I've ever owned whined to some degree.

One thing to note, the stock Pirelli tires will start to whine/make noise after 10,000 miles. They'll just get worse and you'll swear its the rear diff. Its the tires. Big difference in sound once I replaced the stock tires.
 
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