Happy holidays all. When driving in 4wd hi/lo I started to hear a clunking / thud noise sporadically. Driving on wet/compact snow and it sounds as if coming from under the cab of the truck. Appears to drive okay, however, curious to know any possible problems that might be causing this and if safe to continue.

 

Stretched out chain in the t-case, or some bad u-joints in the front shaft.

 

Keep an eye on t-case lever. I replaced motor mounts in a '99 because customer noticed the t-case lever moved around a lot with throttle.

That said, I don't recall a "clunk" per se and you'd typically observe this in either 2wd or 4wd.

A bad wheel joint (u-joint) can also cause a clunk in 4wd. You wouldn't think so but I've seen it.