I have a 99 XJ and installed a RE 3.5 Superflex kit on it and it has an occasional rattle when you let off the gas. It sounds like something loose but I checked everything and it's ok. This only happens when you let off the gas and when you accelerate it goes away instantly. It sounds like it's in the front or middle of the Jeep. Any thought's???

 

I've got the same kit, and the same noise on my 97. I don't hear so well anymore, but my son was up over Thksgvg, and he said the noise is coming from the area around the transfer case. I can't find anything wrong, but I'm wondering if the noise is generated by the front U-joint of the rear shaft, caused by changing the angle on old joints. One of my next projects is to replace all joints with greasable, high quality HD joints. I guess we'll see what happens. No solution for you, just to let you know it's not only your Jeep.
Bob

 

Sounds like the problem I had, found that I needed to lower my transfer case 1.5" to get the yoke seated in to the transfer case out put shaft.

 

I am about to replace my rear drive shaft with a C-V joint one and at least the joints in the front one. I will drive it without the front shaft and see if the noise is still there, to at least eleminate one thing. Thanks guys.................at least now I know im not the only one.

 

I would suggest a slip yoke eliminator kit, just google them. this should eliminate the vibration that you are describing.

 

I hae talked with Tom Woods about SYE kits and double cardan driveshaft. I think that is the way to go was going to just try the new driveshaft first. Here's some good info on them http://www.4xshaft.com/index.html