Rear Vibration when I let off the gas??

[benzor]

Hi Bimmers

I hope you're all well.

I've been puzzling over a rear noise & vibration for a while, and unable to diagnose.

When driving, if I let off the gas entirely, I get a constant pitch noise and vibration from what feels like the rear. Happens at almost all speeds above 5mph. At highway speeds, it is more pronounced 50-65 mph, and I think it also resonating with the rear plastic trunk bay panel. That said, it is still present if you prop something heavy against that panel. Noise goes away right away if you apply gas.

I thought for a while that it was a stuck brake caliper, but it doesn't noticeably change when you apply the brake. I've also just replaced both rear calipers, rotors, pads, and brake lines, and the rotors are not extra hot when measured afterwards (I did have a previous stuck caliper).

Car has new transmission fluid and filter, and shifts fine.

Some other thoughts I had :
- Would a bad rear driveshaft bearing cause this?
- Rear differential bearing? Got new fluid in last 20k miles.
- A bad axle? Axle boots are intact.
- Rear wheel bearing? No noticeable noise when you turn, which I thought was the main test.

Vehicle has 129k miles, '07 X3.

Welcome your thoughts on how to replicate / diagnose.

Benzor

[benzor]

Welcome your thoughts! Any guesses?

[jclausen]

You need take the car to the shop have them lift it and run it while it's up in the air

[benzor]

Thanks for the thought.

[FaithfulBMW]

Hi Bimmers

I hope you're all well.

I've been puzzling over a rear noise & vibration for a while, and unable to diagnose.

When driving, if I let off the gas entirely, I get a constant pitch noise and vibration from what feels like the rear. Happens at almost all speeds above 5mph. At highway speeds, it is more pronounced 50-65 mph, and I think it also resonating with the rear plastic trunk bay panel. That said, it is still present if you prop something heavy against that panel. Noise goes away right away if you apply gas.

I thought for a while that it was a stuck brake caliper, but it doesn't noticeably change when you apply the brake. I've also just replaced both rear calipers, rotors, pads, and brake lines, and the rotors are not extra hot when measured afterwards (I did have a previous stuck caliper).

Car has new transmission fluid and filter, and shifts fine.

Some other thoughts I had :
- Would a bad rear driveshaft bearing cause this?
- Rear differential bearing? Got new fluid in last 20k miles.
- A bad axle? Axle boots are intact.
- Rear wheel bearing? No noticeable noise when you turn, which I thought was the main test.

Vehicle has 129k miles, '07 X3.

Welcome your thoughts on how to replicate / diagnose.

Benzor

When were the tires changed/rotated/balanced? Does the noise occur if you press the brake and accelerator at the same time? I am suspect that it may be a tire issue which changes when the tires go from a loaded (accel) to unloaded state. My RWD vehicle had some cheap tires which wore unevenly and created similar effect at 35 and 70 + mph. Might be a ball joint or suspension bushing to suspect as well.

Driveshaft doesn't seem like a likely failure mode and would also be pronounced under engine power. Diff bearing and Axle I cant say as I haven't had an issue on any car with those. To check the rear wheel bearing you can lift the car with a jack like you would change a tire. As it is, put hands on tire at 12 oclock and 6 oclock and push/pull and wiggle it and see if you can get wiggle/wobble out of the tire . A bad bearing will feel loose or wobbly. A good bearing shouldn't move much if at all. Do the same with the tire in the air and your hands at 3 oclock and 9 oclock. Vert and horizontal test. Hope this helps, good luck!

[X3456]

I would agree with the above accessment...I was thinking bearings but bearings are not known for failure on these cars pretty much but there's always an exception.make sure you check back with your remedy and findings .
Cheers!

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[norstarguru]

Had the same problem on my x4 .... after much looking and 2 shops- you ain’t gonna believe this - the other two shops had bad tire balancers- I took it to Carmax and they balanced the rear tires- problem resolved!


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