xj makes clunking sounds in reverse?

Hey, my truck makes a loud clunking sound in reverse. It clunks faster, the faster you go. Note this is only in reverse. I have a 3'' lift, but it probably only about 2'' in the back. Its louder in 4wd also. What do you think this could be? It's a 98 if that helps. Thanks

could be a bad u-joint

I had the same experience when I first got mine. I had no fluid in my transfer case so I filled it up and it didn't help. It was either a transmission or TC problem. Mine was the AW4 and it was replaced with the same AW4 and 231 combo. I assume however it was transfer case related. I think the chain was stretched out on mine.

To me it sounded like I was driving over bricks that were laid with the corners up.

Either way, check out your transfer case.

I think I'm going to try U-joints. Well actually, I'm just going to pick up a used driveshaft for $50. But I'm wondering... why would it only do it in reverse? wouldn't U-joints do it all the time?
Also, the clunking happens every time its in reverse (not just sometimes) and it won't do it unless it's in gear with the clutch engaged.

BTW, I have an ax15 trans if that helps.