the control arms on ZJ's love to clunk, wait till you take it offraod. of course if you suspect a bad u joint just crawl under and check with it in nutral and the parking brake set, shouldn't take more than 30 seconds. i beilive your ZJ has a solid nondisconnecty front axle, meaning that the front drivshaft is always spinning. when in 2wd there should be absolutly no power being tranfered through it though.