At least I think it is. I've had a clunk/thud that sounds like something is moving around in my cargo or back seat area since I bought the jeep. I figured it would go away when I did my 4.5" iro lift. It didn't.
I found that if you bounce the back bumper up and down a few inches you could get it to make the noise only much more softly than when you drive it.
I got my neighbor to bounce the bumper while I was under the jeep so that I could find the problem. I found out that the noise and thud are coming from the tcase. You can feel the thud in the driveshaft and tcase but not in any part of the suspension. The driveshaft only moves into the tcase about 1/4" since the suspension is only being compressed a couple inches. Also I can't seem to get it to make any noise or thuds by grabbing the drive line and trying to move things.
At first when I found all this I thought the ujoints were bad but I don't get any typical ujoint problems (vibration on decel, loose driveshaft, etc).
Anyone ever experience this?