[mal10015]

Hello, asking y’all to play internet mechanic with me and help me get some insight. I just purchased an E91 xdrive last night private sale, and on the way home there was a vibration and humming coming from the rear of the car. When I first took the car out for a test drive, the vibration was there but it was very faint, hardly noticeable and I assumed it was just unbalanced wheels and tires.

Then after I handed the cash and drove the car home, it started happening right when I hit 40 mph. Had my buddy who came with me to pick it up drive it, he assumes rear wheel bearings.

So now the kicker: this morning I rotated the tires for giggles to see if anything changes. Took it out on the connector near my house, everything was good, the front instead had a little bit of shaking, but the rear was smooth. So at this point I figured the wheels and tires need balancing. I go get an emissions test done, then after getting gas the problem starts back up again. Now I’m stumped because the problem went away, now it’s back. The vibration doesn’t change under load, but it’s constant once you hit 40 mph+ and doesn’t go away even after hitting 80.

Any thoughts or experiences? So far potential suspects:
Guibo, center support bearing, rear wheel bearings

Tl;dr:

Bought E91 xDrive
Vibrates from rear after hitting 40mph and continues
Rotates tires
Vibration in rear gone
Drive a little more, vibration comes back in the rear
Vibration does not change if I press the gas more or the car is under more load.
Car pulsates like crazy like the rotors are extremely warped when braking

____


Edit: took the car out for some errands over the weekend, strictly drove local roads, didn't go higher than 45mph, and the car was perfectly smooth. Ruling wheel bearing out of the equation, suspecting driveline related issues.

Suspects remain guibo, center support bearing, adding u joint (are the E9x xdrives replaceable?) and potential sticking rear caliper per Cal122

[Cal122]

Add to your list to check if you have a sticking rear caliper that might be intermittent. It happened to me on my recent purchase and neither the dealer (recall work) or inspection caught it. I figured it out after I noticed one wheel was giving off heat after driving and there was much more brake dust on the one wheel. Fixed after having the brake caliper replaced, new set of rotors/brake pads and of course flushing the brake fluid.

[mal10015]

Originally Posted by Cal122

Add to your list to check if you have a sticking rear caliper that might be intermittent. It happened to me on my recent purchase and neither the dealer (recall work) or inspection caught it. I figured it out after I noticed one wheel was giving off heat after driving and there was much more brake dust on the one wheel. Fixed after having the brake caliper replaced, new set of rotors/brake pads and of course flushing the brake fluid.

You know, I did notice some burning smell coming from the rear after driving the other day, I'll definitely have to check that. But at the same time, I wonder if it's truly the rear brake caliper sticking if the vibration and pulsating starts after I hit 45+ mph and it continues from there. Regardless, wouldn't hurt to check

[Tambohamilton]

All tires in good condition, correctly inflated and correct size?

[mal10015]

Originally Posted by Tambohamilton

All tires in good condition, correctly inflated and correct size?

Yes to all. Like I mentioned in the OP, I rotated the tires to rule out the wheels/tires being the issue. I am now convinced it has to do with the driveline, but don't have the patience to lay down on the ground in freezing weather to investigate. Would like to see if anyone's had a similar if not the same experience before I bring it to my buddy who has a lift.

[Cal122]

Originally Posted by mal10015

You know, I did notice some burning smell coming from the rear after driving the other day

Yes forgot to mention the smell too, although it wasn't a lot. In my case it also wasn't really noticeable until I was on the highway (you could see vibration in the rear view mirror too), but even then there were times it would disappear so I originally thought it was the tires or a wheel bearing.

[mal10015]

Originally Posted by Cal122

Yes forgot to mention the smell too, although it wasn't a lot. In my case it also wasn't really noticeable until I was on the highway (you could see vibration in the rear view mirror too), but even then there were times it would disappear so I originally thought it was the tires or a wheel bearing.

It doesn't seem to be a stick rear caliper, or at least it doesn't show any of the typical symptoms other than the smell.

The car still drives perfectly normal when driving on local roads, been taking it out to run errands around town.