Hello
I have a 2003 chevy avalanche 1500 with a 5.3 and 130xxx miles. It does have a gov loc rear end. I'm haveing some noise problems with the gov loc. whenever I'm on icy/snow terrain, the rear end makes noise. There is a clunking noise when the gov loc engages/disengages- I'm not familiar with how they work. In all other aspects the rear end is working fine. I just hear noise when the tires start to slip and the rear end kicks in.

I changed the fluid and replaced it with 75-90 synthetic. I have put on 200 miles and no change. In doing some reading some guys run 80-90 in the read ends- no additive as it creates less friction on worn out clutches????

Any thoughts on what could be happening or insight on fluid. The manual says 75-90 synthetic- which is what I put in.