I have a 2000 jeep grand cherokee 4.7V8 quadratrac with 100k miles. All time 4wd seems fine. I'm having a loud clunking sound when in 4low. It sounds like its under or behind the center console(transfer case area). When the manual transfer case selector is in neutral there is a clicking sound that if I had to guess is coming from the same spot. I've been under it, all the CVs and Ujoints feel good, but when I rotate the front driveshaft by hand (less than 1/4 turn) I hear some clanking, and rattling sounds from the transfer case. It sounds like something is broken inside, but I'm not overly familiar with jeeps and those could be regular sounds, even though I don't think so. Transfer case oil has never been changed, or has only been changed once long ago. The problem began recently in a big snow and cold temps(20° or less).

So, any ideas on what it may be? I know the transfer case is an obvious possibility, but I wouldn't mind exhausting some less expensive options first. A little research makes me want to adjust the linkage, and change the fluid.