It's typically solved with a change of fluid plus some friction modifier additives.
This specifically addresses diff noise in slow-speed turns.
P/N 832 222 82 583 SAF-XJ + FM booster
Plenty to read here:
http://www.m3forum.net/m3forum/showthread.php?t=86605
NOTE this change may not necessarily cure all cases of differential noise/grinding, YMMV.
regards
rob