Sounds like you have the infamos piston slap/knock problem. I had it and lived with it for about 18 months until it got so bad that I could not stand it any more.
I had my engine rebuilt at 168,000 to get rid of it. The 4.0 is pretty well noted for this problem.
Previous Jeeps: 84 CJ7 (A True Jeep), 2000 XJ (163,000 Miles/Totaled (Pictures of wrecked Jeep in gallery)), 2004 WJ (parting out die to major electrical issues)
If you don't have time to do it right the first time, how do you have time to do it over.
Lifetime member #13
2011 Tango/Mango JKU