BMW M6 Problem Report
BMW M6 Rubbing Noise From Rear Differential When Turning
During tight, slow speed turning, a rubbing noise can sometimes be heard from the rear of the car. This noise is likely coming from the clutches in the limited slip differential. If the noise persists, the differential fluid can be replaced with a special oil available from BMW. On higher mileage vehicles, this noise may never be eliminated unless the differential is replaced.