Tim
Do a search there have been a couple of threads on this.
People (me included) started using heavier weight oil 90w120 I think from memory to make the diffs quieter.
I have since reverted back to the standard 75w90, as I found no reference to heavier weight oil when I searched the American supra forums about the weir kits, and felt it was the wrong thing to be doing. Heavier oil adds to the drivetrain power losses as well.
Mine quietened down after a while.