This literally started happening to my 2018 LR M3 RWD with ~71K mi. this past Thursday. It became embarrassingly loud within a mere 3 mile drive. Yikes. My awesome EV sounded like an old rust bucket. I immediately came on this forum to research it, as well as YouTube. It seemed the upper control arms were the culprit. Along with that I also saw a few videos demonstrating a few quick DIY fixes. Injecting grease into the rubber boots of the upper control arms or removing the wheel and removing a bolt from the knuckle area and articulating the joint manually to redistribute the inner grease were the two main cheap DIY fixes. So I went to AutoZone, bought a $8 red grease tube, a $20 grease gun, and a $5 grease gun needle attachment. I followed the instructions in the video below, but I was able to reach the grease depleted rubber boots (see attached before and after photos) while the car was parked normally, so no need to lift.
After filling up both front upper control arm rubber boots, I tried massaging the grease around with my fingers. The sound was minimized, but still there. Made a Service appointment in case my DIY fix didn’t work. Closest appointment was a week, so I had that long to figure something out. BUT after driving around over the weekend, about 100-150 miles, it started going away little by little. I think being rough with the suspension helped, so maybe going over a few speed bumps or a bumpy road might help spread the grease around. Now, Monday just three days after the sound started, it’s completely gone.
Canceled my service appointment. Out of warranty repairs don’t have to suck. Good luck fellow DIYers.