Originally Posted by quixs1lver
A grinding noise may be heard coming from the differential during slow cornering. This noise is best heard during tight cornering situations; for example, while parallel parking, driving in a tight circle, etc
When the rear wheel speed differential varies during tight cornering, a slip stick effect is created on the lining and steel discs incorporated in the differential locking clutch, causing the grinding noise.
This noise typically goes away as the locking clutch discs in the differential are broken in.
The break-in time varies depending on driving habits; for example, tighter cornering (working the locking clutch) means that it takes less time to break in the locking clutch discs.
IF THE TECH CAN VERIFY THAT THIS IS THE NOISE differential oil should be replaced with: 83 22 2 282 583 Special differential oil kit
e46 differential = e92 differential with bigger cooling fins. there has been a small percentage of people who have had concerns on slow tight cornering such as parallel parking a groaning type sound is heard from the rear differential. Since this is a same issue known with e46 m3, e60 m5, e63/54 m6 and e90/92 m3. a 'special' differential fluid is used
"In principle, the final drive is assembled in the same way as in the E6x M5/M6. It is, however, a separate new development. The bevel gear shaft bearing is a frictionoptimized, double-row, angular-contact ball bearing. The gear ratio between the bevel gear and the crown gear has been adapted to the engine speed and gearbox ratio of the M3.
The final drive ratio is 3.85:1. The 215 gear set (crown wheel diameter 215 mm) has been temperature and noise optimized. A friction-reduced gearing is used. The housing of the final drive has been adapted to accommodate the double-row angular-contact ball bearing. The flanges for the propeller and drive shafts are the same as those used on the E6x M5 and M6." BMW Aftersales Training
Thanks for the info on the diff oil. I need to take mine in, as it continues to be noisier than I like. As I said in the OP, it didn't start until the oil was changed at first service.