So just recently I installed some diff collars on my car and it made a huge difference overall with feel of the car when its being driven but now I have started to notice this humming/ whistling noise coming from the rear of the car. It doesn’t happen all the time. I have noticed that it only happens after 3k RPM and at highway speeds. Also the noise only happens when you gently let off the throttle. If you are accelerating, than it is fine but its only when you let off the pedal slightly is when you hear the sound. It doesn't happen if I'm in nuetral coasting or under 3k rpms. Doesn't happen when I let the clutch out either. It just started after I put the collars in. I have a AP2 w/ 133k miles.

Any help is appreciated.

 

I would think with stiffer mounts, more sounds resonate through the chassis. Obviously these are noisy cars from the beginning, and just stiffening any part of the car will amplify it(mounts, suspension, etc.).

 

See I called Evasive and talked to them since the sell a similar product and they said the same thing as well. I dont want it to be something major. I mean everything feels right with the car. I swapped the wheels and that made no difference. I got underneath and rechecked all the nuts and bolts and they are tight so maybe I'm just worrying about nothing.

 

This is pretty common with solid mounts of any sort. Solid engine mounts make a car "undrivable" for some people. Personally, I think solid diff mounts are worth the trade off.