So I was driving at a high speed in my 2016 RT when I started hearing loud metallic rattling sounds.. i got worried and slowed down and the driving felt a little “off”..
after thinking it over I (in the interest of learning) accelerated again to instigate the sound...apparently going 110 Mph is guaranteed to instigate that sound, though the “off” sensation of the driving didnt repeat... any theories or similar experiences?
Wind becomes a factor at speed. (As an ex-motorcycle rider, and only with "naked" motorcycles (no fairing) I can tell you that above 100mph the wind blast becomes substantial.)
A loose plastic panel or other part under the car, in a wheel well, can get pushed out of position and can come into contact with something else: road, mechanical part (something relatively stationary or even moving/rotating like a diff or axle shaft); which accounts for the racket. The racket might be compounded by less than ideally balanced wheels/tires or if you have fitted some other tires other than those sanctioned by the factory lousy tires.
(Years ago I heard an odd sound at speed. Turned out the leading edge of a front wheel liner had lost its fasteners and at speed the force of the wind pushed the leading edge of the liner down against the road. The leading edge of the liner clearly showed signs of abrasion. And it is not that rare of an event for me to spot a car with some under body panel hanging down even if the car is not moving very fast. )
The "off" sensation was probably (and not unexpected) just your imagination. More than once with other cars and not even at 100mph+ I've felt the car "off" to the point I'd pull off the freeway to check the tire pressures (this before TPMS) only to find the tire pressures on the money. Just a combination of the road surface, the wide and in some cases rather worn, tires and my imagination fueld by the "fear" of a flat tire.
To get to the bottom of the behavior from your car will take work. It is not practical to try to diagnose the symptoms at 100mph+. At lesser speeds sometimes a good video made of the car can spot a wheel/tire obviously moving too much due to a balance or tire problem. Or possibly a plastic body panel being forced out of position due to the force of the wind.
But to have one car traveling at 100mph+ and a following car close enough to make a good video from first behind then from in front of the car is another thing entirely.
More practical is to get the car in the air and make a careful/close/thorough inspection of the underside of the car looking for any signs of a panel being loose -- missing fasteners is a good sign -- or signs of it having been in contact with something else.
Give the panels a tug if you can, push and pull them to see if you can find one you can move about. Look for any loose hydraulic lines, hoses, parking brake cabling, anything loose not properly secured.
On the driveshaft look for any sign something has been touching it and there is a brighter or burnished spot/ring around the driveshaft. If the rear end has exposed half shafts check them too.
In the wheel wells look for any signs of tire contact with the body or wheel well liners.
If you find nothing up to you if you want to go to to the trouble of having the wheels/tires balanced with the hope you find a wheel out of balance or possibly a tire with something wrong (internal belt failure for example) that results in the tire performing badly at higher speeds. This latter condition might be brought to light using a road force balancing machine.
There is also the possibility alignment might play a role. But it is last because the odds are slim. So it would be up to you if you wanted to go to the expense of having the alignment checked/set. There is also unfortunately the risk the alignment can be made worse. I have not had to have my Hellcat alignment checked/done but with previous cars it is important to use a place that knows how to properly aligned the car, has access to the correct settings/adjustments, and can provide a before and after printout that shows what the settings were before the alignment and what they are after and for each setting show where it is in relationship to what is ideal and what is within spec.