I went on a short trip a few nights ago with a friend and the trail was great until numnuts broke somethig on his yj cuz he doesnt no how to build a jeep :/ any way, got back on the road and noticed a banging, somewhat vibrating sound. This was not there before wheeling.
The slip section on my front ds was wiggling so i replaced it and put a new u joint in- still there. The rear ds u joint at the axle end seemed to wiggle a bit between the little stops on the pinion yoke so i replaced that- still there.

Ill try to explain, its not constant. I notice it most at low rpms in 4th gear, when i push the throttle, its a vibrating sensation i can feel at my feet.

Ive gone under to inspect but nothing stands out to me.

Any ideas? It a 5spd with about 3" of lift with 33s.

 

something get bent underneath?

 

I had a similar problem and it was my tailpipe clunking around

 

Its so intermittent, and nothing looks bent or damaged, but it does seem like a driveline issue.