Having looked at a lot of these threads, it seems pretty rare for the sound to be from the front motor, particularly since it's not typically being used at steady state speeds. I think I may have mentioned turning down the rear seat backs, that's so you can better determine if it's front or back. Obviously, if it sounds louder when seat backs are down, then it's the rear. The issue is the glass is so reflective, sometimes sounds from the rear seem like the front, and vice versa.
A bit surprised they didn't change the ground strap to begin with, which implies that the strap is the current braided one, and not the original solid one which seemed to be more problematic.. On the other hand, when I had my 3 in the Service Center for the first time and I talked to the service manager, he said there was a sound from the rear inverter but it was within spec. I told him to go ahead and change it, even if it cost me. He went ahead and changed it, and, even though he said it would cost me and might not change the sound; in the end, there was no charge. And, yes, the sound is gone.
