I have a 1995 and am getting a humming noise like riding over rumple strips. Once I slow down to about 5-10 mph I get a clunk. After that all is fine. Ive only had it do this in a straight line so havent been able to test it in curves. It does not do this all the time. I could go a few days or weeks before it does it again Then again it could do it 4 times in a day. I have checked for play in the wheel while having it jacked up and nothing all seems tight. When it clunks it acts like the 4 wheel is dis engaging was my first thought. Ive read the boards and seen where it could be anything from a vacumn line to bearings to a hub to an actuater. Can anyone add input to narrow this down.

Thanks

 

Check out this thread:
4wd Front Axle Clicking When in 2HI - Goes Away when in 4HI/4LO
I'm betting that your front axle is trying to engage either from a sticking cable or from a bad vacuum switch on the transfer case.