So I discovered a loud rattle noise upon startup of my XJ. I will not assume I know the culprit but it defiantly sounds like muffler, or inside exhaust. However when I get under it while running I can't seem to pinpoint location. Doesn't appear to be a knock though I'm not ruling that out yet. When its warmed up seems to quiet down though and smooth out. When I shut it off at the point when engine dies it almost sounds like another slight rattle. Could this be something drastic like lower motor problems. Camshaft bearing or something like that? I'll keep looking I hope its just heat shield or exhaust doing this but figured I ask and I know I didn't provide much information. If you have any ideas for me to try I would be happy to. If it helps its a 1989 and she starts hard too. Mind you I have not done a full tune up yet. I have everything to do it just have no time right now. Sometimes it cranks over longer than expected to finally fire up. Timing?

If it sounds like its coming from underneath, check the heatshield. The tack welds can fail and cause one hell of a rattle (usually at low rpm, but not all the time). It could even be the cat starting to go. It could even be a loose and/or cracked flexplate. Check the bolts to make sure they are tight. Check the transfer case linkage, anything that moves, really. If it sounds like its coming from under the hood, lean in close to the distributor. The distributor bearing will wear out and start to wobble over time. Remove the cap and check the shaft for wobble. It shouldnt move at all. the pulleys can make funny noises, too. Even the water pump.

Without being there, its hard to say what it is. Buy yourself a stethoscope and start poking around. You can get them for 5-10 bucks at most parts stores. Or you can use the end of a screwdriver or even some rubber hose. Put one end to your ear and the other to whatever it is youre listening to.

Thanks for the advice I'll keep poking around and maybe I can get a good video sound clip to hear it. Not sure it will help you guys identify it but where is the heat shield I should be looking at?

One of my thoughts was the cat too.

Rotted exhaust isolator.

Where would I find this?

(not my pic)

Thanks right after I asked I took a look on a google search and came up with same photo lol. I'll look on my XJ tomorrow see what I find.

So when I got home today I climbed under XJ to see if mine had the bracket exhaust isolator and mine didn't look like the one in photo. Exhaust was hooked up to a bracket near the transmission cross member but no signs of a rubber bushing. Plus when I started it didn't appear to be coming from that area. Still on the search for the noise seems closer to engine though and again clears up mostly when warm.

Then when it is shut off right at the point when its off it rattles then silence.

Any ways I'll keep looking just figured I would update that nothing new

Pull the dust cover and check your flexplate and torque converter to see if those are nuts are loose. It's a known common problem.

Bang around with a rubber mallet down there to find out whats shaking.

I have the same symptoms and have not had time to look for it yet so if you could post what you find that would be awesome!

Feel free to use this: