Hmm. I was just getting ready to post about the same problem on my 2000 XJ. I tightened the rear most exhaust hanger as it was loose. Still had the sound. Then it went away for the summer. Sound came back last week. Just went and checked everything suggested here and still have the sound. It is coming from way in the back of the XJ.

 

Spray the threads of the rearmost clamp bolts with penetrating oil and tighten them again.

 

Since this seems to be a community thread......


With my '98 Xj I have a vibration at idle as well.
I just replaced my header (APN) a few months ago. (felpro gasket and doughnut gasket as well) And Mudfrogs cat back kit. The only thing that's stock is the down pipe. I also had a flexable pipe put in where the pipe goes straight across from ds to ps.
I replaced all three mounts over the summer too. But mine isnt a rattle per say... Im fairly certain this could come from the engine. Could a dirty IAC have anything to do with this? Any other suggestions folks?

 

I think I found my rattle. Loose license plate. One screw was missing and causing the license plate to vibrate and rattle against the lift gate.

 

Well, that's a new one!!

 

I had the exact same problem as the original poster and it turned out to be not only bad motor mounts, but an absolutely destroyed transmission mount. Just my 2 cents.

 

Can be lots of things. That's why those wondering should go do some "noggin pokin'" under their Jeeps more often.

 

Damn. I'm having the same issue right now. Can't find the problem. So annoyed.

 

same thing right now for me. Just had motor mounts and transmission mounts or whatever replaced on my lifted 2000 cm. They were so shot that now my drive angles are so different and when you stop at a light or whatever and are on the brake its vibrates the jeep so bad everything shakes. If you put it in park quick and back into drive while you're waiting it doesnt do it again until you stop again. Could my driveshaft be out of whack now?

 

You should probably start your own thread. Vibrations could be caused from different things. There is no reason to think that your cause was someone else's. Link your motor and transmission mounts. Some isolators/bushings/mounts are intended to create more vibration that others. Idle with the transmission fighting the brake would be the peak for vibrations. When you post your own thread you can also attach images of your mounts for reference with the links.