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Discussion Starter #1
Ever since I got my car back from the dealer (transmission replaced and exhaust removed), when I remote start the car, there is a really loud rattle coming from under the car. It sounds like it is pretty far forward on the car, like up by the cats. It only lasts a few seconds, and it appears to go away as the butterflies close for the active exhaust, and only seems to do it on cold starts, not when starting while still warm after running. I've crawled under there, and am not finding anything obvious. I'm probably going to have to put it in the air, cold, and lay under it while starting it to see if I can find it, but I figured I'd see if anyone else had this experience, and had suggestions.

Thanks.
 

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what kind of rattle?

is it a sewning machine sound, a can rattle, or like a card in the spokes of a bike?
 

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Discussion Starter #3
Of those three, I'd say it's a rattle can. When I first heard it, I assumed it was a loose heat shield on the exhaust, but I'm not seeing it. It sounds like a loose piece of metal, vibrating against a piece of metal, but it goes away soon after starting, and I can't seem to make it happen with the throttle.
 

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Of those three, I'd say it's a rattle can. When I first heard it, I assumed it was a loose heat shield on the exhaust, but I'm not seeing it. It sounds like a loose piece of metal, vibrating against a piece of metal, but it goes away soon after starting, and I can't seem to make it happen with the throttle.
Could it be a loose catalyst, maybe they dropped one of the mid pipes and damaged it during install? Have you tried tapping the exhaust near the cats with a rubber mallet while the car is cold. I thought maybe the manifold to midpipe clamp but you would hear exhaust leak.
 

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Discussion Starter #5
What kind of shields do the converters have? I wonder if there is a loose shield, that stops being able to vibrate and rattle as it heats up. It seems to only do it when the car has been sitting for hours.

Does anyone have pictures of the converters off the cars?
 

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there's heat shields attached to the body, all along from the trans tunnel and up to the rear axle.

Not shields attached to the exhaust system or cats. On the active exhaust versions
* '15+ 6.4, 6.2SC
* '17+ 5.7s now have these

there are shields between the AES actuator and the pipe, but that's about it (see image)
 

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Discussion Starter #7
there's heat shields attached to the body, all along from the trans tunnel and up to the rear axle.

Not shields attached to the exhaust system or cats. On the active exhaust versions
* '15+ 6.4, 6.2SC
* '17+ 5.7s now have these

there are shields between the AES actuator and the pipe, but that's about it (see image)
I saw one of those shields loose up under the driver's seat, and reattached it, but that didn't stop it.

I need to figure out what it is. It's driving me crazy, and it's embarrassing.
 

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I saw one of those shields loose up under the driver's seat, and reattached it, but that didn't stop it.

I need to figure out what it is. It's driving me crazy, and it's embarrassing.
The heat shields are a some sort of soft aluminum and not steel like in the olden days. Check the connections of your mid pipe

Capture.JPG

but if the noise goes away after car gets hot could be a busted cat. Like I said, if it was on a lift and they were re-installing the exhaust the mechanic could have dropped the mid pipe and cracked the ceramic inside the cat. You can do what the guy did in the vid below and record the sound near the cat at start-up, or you can tap the exhaust with a rubber mallet to see if you can hear something rattling in the cats, or take it back to the dealer.

 

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There are 2 bolts that get bolted into the body right in the middle beneath the exhaust. Check those bolts.
If you look at the area where the red bracket goes under the exhaust that's where the bolts are. If they're not tight it'll make the ratting noise. Especially when the exhaust system is still cold.
 

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May not be of help to you but about a week after I had my Borla ATAK cat back installed, I developed a similar rattle. It wound up being located on the left side active exhaust. The little metal "cylinder" that is attached to the spring had way too much play in it and rattled until the car warmed up.

So if they had to remove your exhaust they would have had to disconnect the active exhaust from the exhaust piping so maybe something in that area is rattling? Initially I thought the sound was coming from towards front as well but after hitting the pipes for a few minutes, I found it was there.
 

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Discussion Starter #11
It really sounded like the video that ChallyTatum posted, so I got under there, and banged around with a rubber mallet, since just shaking things wasn't finding it. The main sound came from the join between the headpipes and the mid-pipes, so I started the car while I was under it. The sound was definitely coming from that area, and as I was listening from leaks, water started bubbling out of those joints. I tightened them as much as I could, and will see how it sounds after everything cools. I may need to tighten it again when cold, too. That spot gets pretty warm, very quickly.

Anyway, thanks to everyone that responded. Hopefully that's all it was. I'm really surprised it was as loud as it was.
 

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Even fully tight the condensation will still escape at the joints. Good call on the rubber mallet.
Careful tightening the band clamps. You don't want to over do it as it will distort the pipe and (1) will be a bear to separate in the future and (2) can actually cause the joint to leak. I think max torque is like 40-45 ft-lb. With these slip-on connections it is difficult to make them water tight without applying a thin layer of high temp silicone on the inside of the female pipe. You don't need much silicone just a very thin covering. BTW the mid pipe to x-pipe band clamps are tack welded to the pipes.
 

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Well I was hoping to get to it tonight but, it does not look likely right now. Hopefully soon though, as if this does not fix it, it goes off the road in Oct. and will not be out until April and I do not want the warranty up if it is something else, but then again I could always get it warmed up so it does not make the noise and trade it in or Carmax it.
 

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Ever since I got my car back from the dealer (transmission replaced and exhaust removed), when I remote start the car, there is a really loud rattle coming from under the car. It sounds like it is pretty far forward on the car, like up by the cats. It only lasts a few seconds, and it appears to go away as the butterflies close for the active exhaust, and only seems to do it on cold starts, not when starting while still warm after running. I've crawled under there, and am not finding anything obvious. I'm probably going to have to put it in the air, cold, and lay under it while starting it to see if I can find it, but I figured I'd see if anyone else had this experience, and had suggestions.

Thanks.
982475


You need the spring like part found here on the actuator. It’s $25 at the dealership and should only cost $20 to have a mechanic put it on for you.
 

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Hard to believe that the exhaust flap/springs which are near the back end of the car would sound like they are coming from the front of the car or cat area.
 

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Discussion Starter #20
It was definitely the connection between the headpipes and midpipes. The dealership had the exhaust off, and didn't tighten the band clamps adequately, so they rattled against each other for the first few seconds, until the heat and water swelled cushioned them enough to quiet them down. Tightening the clamps fixed it. It was fixed until the next time the dealership removed the exhaust and it happened again. So, I tightened the clamps again, and it's been fine since.
 
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