I just bought an e-bay '99 XJ and when it sits at idle there is a rattly wobble behind the stereo with the air on. It seems to be a really bad place to put a fan and as soon as the car gets above 1200 rpm it goes away. Any ideas? reapirs?

the fan is under the hood on the passenger side maybe you are hearing through on of the vents take it out and clean it out maybe theres something in there making the noise or the fan it self is bad

This may sound strange .... but check your cat ... had a similar issue and thought it was behind the dash or in the trans ... finally crawled underneath and started rapping on the exhaust system ... turned out to be in the cat, they eventually fall apart inside and stuff starts to rattle .... mileage and performance goes down too ... and ultimately the thing just quits. Sucks if it happens to you ...

good luck finding it. mine has the same rattle but to me it sounds like it towards the rear hatch on mine, cant find the noise anywhere, but just like yours, its only at idle

The linkage to my transfer case used to rattle at idle in gear. Lift slightly on the 4x4 lever and see if it goes away.

Good luck, keep us posted

Thanks for all the insight. Looks like this weekend I get to take a tour of the undercarraige. I knew the muffler was on limited life span and it would make sense that the cat would have the same life expectancy. I now have a legitimate excuse to update the exhaust system with a high flow cat and flowmaster exhaust. I'll post what rattles.

Performance and mpg wsnt bad but wsnt the greatest either, though it was my tob or something like the dust shield rattling at idle ended up bein my cat too

I had the same rattle in my 94 xj. I looked everywhere and nothin so i looked at my exhaust and there was a rock stuck between my pipe and the trasfer case cross member. It might sound stupid but have you looked at anything like that?

check all your exhaust hangers also-- one of mine broke, and the pipes were getting into the trans. mount making a bunch of noise.

Mine rattled until I changed the tranny mount. Only did it at idle but it drove the wife crazy and I finally figured it out one weekend while crawling under the thing. They are easy to change with a couple of floor jacks.

This was the problem with mine as well, a couple of new bushings and all is quiet

I did the undercarraige serach and no rocks, debris or shields rattling. Looks like I need new Engine mounts and a few shields need to be replaced from rust corrosion but I friend pointed out the problem when we were out and about. It was the steering. If I turned the wheel, the rattle would go away. I saw a post on the board about the steering linkage rattle and a fix for it. I'll give that a try this coming weekend. Thanks for all the help.