As stated above your angle of your u joints are now not the same causing your driveshaft to vibrate which can be heard through many different shakes and thuds and vibrations and all kinds of stub, most times when you left off the gas, sometimes at other times. You probably will never hear it when you are accelerating because the rear springs are compressed and thus back into the acceptable limits of our driveshaft without vibration. This will cause premature pinion seal leaks if not corrected. 2 ways to correct, upgrade your driveshaft to have one u joint and one cv joint on it, or get adjustable lower links and correct your angle that way.

Reading material:

http://www.pirate4x4.com/tech/billav...ft/index2.html

http://www.4crawler.com/4x4/CheapTri...OperatingAngle