I know nothing on this subject, however the diff was making a rumble (loudly) on a previous car of mine. I believe there were two options. new diff (new, recon or salvage) or try to repair the existing one.
On inspection the 'repair' or thickening of the oil to almost black treacle status had been carried out before to 'firm' it up a bit. It obviously lasted a while and I was none the wiser.
So new/ change of diff it was. Ended up putting in one from a breakers with a guarantee and was excellent. price still steep but no where near a new one.
I guess my point, as im rambling, is when noise appeared it was checked out within a thousand miles or so and fixed within the next thousand or so (work commitments and sourcing the part) but I would get it diagnosed sooner than later and take it from there. See Badbaz ;-)
Hope, if any, that gave you the slightest insight.
Gordon