clunk from rear end... I think

[RVA16v]

Ok so all was well until I mounted new tires and wheels yesterday...went from 235s to 30"s. now there is a LOUD clunk coming from what sounds like the drivers rear, but sometimes feels like its directly underneath of me, its constant with movement. Now, My rear spring packs are dead...flat and dropped down in the front (on the list to be replaced). Previous owner installed a block under them. Is this the axle wrap thing ive been hearing about? Sorry Im still new to jeeps, but am a tech. the U joints have no noticeable play in them, and while I had it on the lift everything aside from the front end, looked ok. any suggestions? shocks are pretty much toasted too, i just dont want to start throwing parts at it, I need it driveable and would like to single out this problem first.

[RVA16v]

After searchin for the last half hour I think Im going to check the drums in the AM and check the U Joints again.. apparently some people had them go bad with no noticebale play.

[RVA16v]

ok...update drums look ok. Seeing as I have always worked on imports (Im a mazda/ VW tech) Im not too familiar with U joint type set ups at all...but, there is a fresh new shiny spot on one of the caps that Im assuming shouldnt be there. I decided to change the fluid in the rear diff while I was under there and that was very low. I just bought this XJ about a month ago and want to fix everything right the first time. Im going to replace the rear U joint, but is there anything else I need to look for??

[hotrodXJ]

ok...update drums look ok. Seeing as I have always worked on imports (Im a mazda/ VW tech) Im not too familiar with U joint type set ups at all...but, there is a fresh new shiny spot on one of the caps that Im assuming shouldnt be there. I decided to change the fluid in the rear diff while I was under there and that was very low. I just bought this XJ about a month ago and want to fix everything right the first time. Im going to replace the rear U joint, but is there anything else I need to look for??

Yes, look for a leak causing your gear oil to be low. Don't mess around with gear oil leaks. I've seen a plastic bag wrap around at the pinion seal to kill it. Within 1000 miles, there was nearly no gear oil left and the ring and pinion were toast.
These are jeeps. They have a lot of different things that may cause a clunk. I've been a jeep dealer tech and chased down many clunks. Not all that many were common. With my own vehicles, I'd certainly start with the obviously bad parts.
Can you get it to clunk when running it on a lift?

[RVA16v]

No man, I had the rear off the ground first thing this morning to check that. started and let it spin... no clunks at all...its def. a rotational noise when the weight is on it though. more so it seems with weight on the tires... I supported the axle to maintain the same angle on the drive shaft (or close to it) and same result, no noises when in gear. It looks like the diff was just sealed poorly, as in maybe they didnt let the sealant cure before assembly and refill. Thanks for the help. I'll let you know what I find, as alot of the "clunk" posts had no results posted.

[RVA16v]

well, replaced the rear u joint...greased and lubed chasis and suspension, changed diff fluid, did a VC gasket while i was at it...test drove and noise still there. got pissed crawled under it and looked around some more....found it! wheel weight was hitting the sway bar... i need some spacers and to ditch the rear sway. solved.