Help please - Grinding sound from transaxle while reversing
 

I have a grinding sound from the transaxle/drive train when reversing. It’s cyclic (grind, quiet, grind, quiet...) and varies proportionally with my reversing speed. It’s done it ever since I’ve owned the car. Recently changed the trans fluid with Porsche fluid and no change. I didn’t find any metal in the old fluid and the correct amount drained out. No problems shifting, no noise in forward gears, no vibrations, no cv clicking.

It’s not a rock in a brake shield, nor a problem with the e-brake. I just put on new rotors and pads, so I know everything’s clear for the brakes. 107,000 miles on the car.

Any ideas???

Jack it up, put it in neutral, spin the wheels one at a time (by hand) in reverse, and see if you can hear it then. That may allow you to get closer to the sound.

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Check the output shaft covers. When I used to autocross my car (hundreds of clutch drops with track tires) I ended up cracking one of the covers. Oddly it didn’t leak but the crack created an edge for the drive axle to grind on. Oddly I now I have a new grinding with a different transmission 5 years later. It only grinds going forwards and doesn’t grind when the wheels are up in the air. Probably once again a transmission problem. The 2.5L transmissions aren’t great for taking abuse

Also check for wheel bearing play. Try jacking up the car and checking for wheel play, you don’t want to push failing wheel bearings too far on these cars. The aluminum hubs are soft and the bearings can spin in the hub when they fail, if this happens you’ll need a new hub as well as a bearing.

Long shot, but my grinding noise was related to ebrakes. I had put on the ebrake after a track session and the pad stuck and dammaged the rotor. The gap between rotor and hub is not a lot and if there is wheel bearing play that might be rubbing.