I have used the synthetic Valvoline Durablend 85W-140 with quite good results. If not completely eliminating differential noise, it greatly reduces it.
I also found that after changing the differential oil once again after the initial filling that not only were the gears much cleaner but with the second application it seemed to be even quieter.
Tip: Make sure the differential fill plug can be removed first, if you can't get that out to refill, don't bother removing the drain bolt.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)