Sounds like a stretched transfer case chain to me.
Crawl underneath the Jeep and grab the front driveshaft...turn it back and forth about a half turn either direction. Listen for the chain slapping the case (you'll know the sound...sounds like light clacking on the bottom of the t-case).
I'm just taking a stab but it sounds like what happened to mine when I neglected to take care of a leak in the case and over time all the ATF leaked out... Give it a shot and keep us posted! (Also check your fluid level)...
Phil M. - Kent, WA
95 XJ Sport w/Stuff
"Who cares about a list of crap, can you drive it?"