My vote is either for a bad lifter, loose rocker arm, or the flex plate bolts being loose. If you have something else to drive, and this will be a trail rig only.. then either buy a used motor now and drive this one till it blows, or pull the engine yourself and tear it down, and teach yourself how to re-build it.
'97 XJ... 4.0 4x4 AW4.
2" budget boost w/t-case drop.
31x10.5 Cooper Discoverer ST's on 15x7 Cragar Soft 8's.
Intake, Ported TB, TB spacer, Super 40 Flowmaster.
Baja Aux. Lighting.
Green Jeep Club #185, Nowhere to Wheel Jeep Club member #1