I have an 01xj automatic trans with 132k on it. When I'm running in 2wd there is no whining, grinding, etc coming from anywhere whatsoever. However, when I put it in 4wd, I get a loud whining/grinding noise coming from the front area, starting at about 10mph on up. I took it to my mechanic and he seemed to think it was coming from the case itself so I put a new/used case in it and still getting the same exact noise. When running it on the rack in 4wd there is no noise but as soon as you get it on the road and run it the noise is there. There are no metal flakes or anything in the front diff fluid. I'm dreading taking the front diff apart, wondering if anyone has any ideas before I go that way? thanks

 

Whining in 4WD "only". Comes from two places. TC or front diff. Sounds like you have front diff. issues.

 

Check your tires for being the same exact brand and size and amount of wear and inflation What you may be hearing is a tcase that is just working hard.