Okay it can be several things. I have the same problem and still can not find what is wrong but I will try to help you the best I can. Try the U-joints, CV's, mud in linkage to the transmission, and a loose bolt. Let me know if it is not any of these. I am still trying to find my problem too haha
4 liter in line six, Bestop Highrock bumpers, Warn winch, light guards, grill guard, Westin running boards, Dick Cepec DC-1's on 33" Mickey Thompson MTZ's, pocket style fender flares, d-rings, hard top, tinted windows, a completely redone sound system with Alpine Type S in rollbar, Arc speakers in the dash and an Alpine headunit, Iggee's seat covers, 3" suspension lift, MBRP Exhaust System, IPF fog lights, steering stabilizers, a woofer, 12" ported Rockford Fosgate subwoofer and amp.