I would love to get to the bottom of this.
I have the popular clunk in my '06 LJ Rubicon Auto, RE 3.5" short arm with 1.25" BL & 1" MML, adjustable uppers front and rear. It is almost reproducible when accelerating in first from idle. Sometimes you can hear it when letting off the gas only in first, high RPM's. With several speed bumps in my neighborhood I hear it very often and it's driving me up a wall.
So far I have checked engine and tranny mounts, flipped rear shocks, tightened exhaust mounts, and found no loose parts floating around in back
It does not occur when turning, which made me think it was the control arm bushings - especially after I read a post about RE bushings failing. I have poly at frame and SF at axle. Tightening to spec this evening did nothing for the noise.
Under no load the rear driveshaft has some play and I have heard conflicting information about how much backlash should exist in a driveshaft under zero load. Some say a slight turn and others say none at all. If I rotate the rear shaft under no load it makes a strikingly similar sound. Could it be internal to the tranny or TC? A chain that needs adjustment? Rear-end? Hard to believe the issue would be internal on a daily driver with under 40K.
I have yet take off my rear shaft and test only front to isolate, but I am willing to bet the noise doesn't occur as there will be no rotational torque to the rear, the place on the vehicle producing the sound (as far as I know).
Any comments/questions provided would be greatly appreciated.