My experience with my 129 was similar. I thought for sure the differential was going to grenade.

Turns out my right rear caliper piston was sticking. The pads were almost to the sensors at that point on that side. The other side's were in great shape.

__________________
Thank You!
Fred
2009 ML350
2004 SL600
2004 SL500
1996 SL600
2002 SLK32
2005 CLK320 cabrio
2003 ML350
1997 C280 Sport