I have a 97 Wrangler Sport, 90k..no lift. When I engage the 4wd I am hearing a loud pitched wine and it does not want to go back to 2wd when I shift it back. Also, this winter when I started using the 4wd I would get a loud repeating thud every few minutes, not all the time...the wine may have been there but I could not hear it becuase the windows where up....any ideas?...thank you..
Have you checked the fluid level, in the T-case? I would check that first, and even change it. If the sound(s) still pursists, it could be anything, from the chain drive needing replacement, to the skid plate mount, needing a new bushing.