check the rear control arm bracket; they can mushroom and loosen the bolts. I had a clunk for a year that I swore was coming from the front. It would bang around off road and when I accelerated into turns. It's a common Jeep problem.

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2006 CRD http://www.UtahPowderCoatings.com/ http://www.gorecon.com/ I'm kind of a big deal.
RL rear bumper, ARB front bumper, Mile Marker winch, Power Tank, Skids by Mopar & Skid Row, RL Super Skink Sliders, 235/85R16 MTR, Air Flow Snorkel, DTT, 4.10 gears, Frankenlift II, Katskin leather, JL Audio stereo, Rosen video.