Has lubing the drive shaft lube points made any difference? Check the oil level in the rear end, it could be low or be contaminated with water which would make it appear milky in color. A noise like you described is usually pinion bearing or ring and pinion ingagement related. I have seen some be noisy for years with no problems, and others make noise for a few days then crap out on ya.

John Luttrell
2001 4x4 short cab, 3 inch lift with 33 inch mudders and Powertrax no-slip in the rear


1991 Jeep YJ, 4 inch suspension lift on 33" BFG's