Please help diagnose rattle/clunk on startup (video)

[yzmuddereffer]

2000 Jeep Cherokee Sport 4.0 4x4 with about 150k.

I'm getting a fleeting rattle (clunk?) on startup, sometimes but not always followed by less obvious rattling that continues for almost a minute. It started doing this about three weeks ago and sounds like it's getting (slightly) worse.

The rattling seems to continue longer and is more prevalent if the Jeep is immediately driven off and turned to the right. Turning to the left doesn't seem to prolong the rattling. It's certainly possible, however, that this turning to the right thing is just in my head.

Symptoms are worse when cold.

I've laid under the Jeep, listened, held my hand on various parts (transfer case, oil pan, transmission, driveshaft, exhaust, etc.) and for the life of me I can't tell exactly where this is coming from. When sitting in the Jeep, it sounds like it's coming from the lower console area and/or under the driver's feet.

Fluids are good.

Here's the video with the camera held in various places. The rattle can be heard immediately on startup. Any ideas are appreciated.

http://youtu.be/-rjSnliawWw

[souske]

Motor and trans mounts are good? If they are original, its highly unlikely...

Pull the chime module next time please. Also, i dont know if its just my phone, but i cant see anything but your ash tray, so guessing 97+, aw4?

[8Mud]

My 96 is making about the same sounds, mine is the Cat converter. It is worse at start up and when the engine is cold, it seems to lessen some when it's hot, maybe heat expansion tightens things up some. My guess is the innards for the Cat converter are loose.

When it gets bad (loose) enough you can bang the bottom of the cold Cat converter with the palm of your hand and hear the rattle.

Some models were on recall for this. The dealership will often deny it or try to wiggle out of it, but the fix is supposed to be free or at worst the cost is partially covered by the recall. Worth a little research, Cats aren't cheep. labor ia always expensive.

[yzmuddereffer]

Thanks, guys. I'll take a closer look at the cat and motor mounts.

My son did take the non-lifted Jeep on an ill-advised off-road excursion early this summer that did moderate damage to the exhaust. Although the rattle didn't show up until recently, that certainly may have exacerbated the problem.

[8Mud]

It sounds like the Cat, but sounds can fool you. The exhaust also has a tenancy to bang on the transmission cross brace. Either from weak engine or tranny mounts or even from the exhaust joints relaxing over time and allowing the exhaust where it crosses over the tranny cross member to sag.

It may also bang in the rear near the gas tank. The rubber exhaust hanger near the axle sometimes rots through and allows much of the exhaust system to move around a lot..

If it is banging on the cross member, I've had some good luck by loosening the two bolts where the cross over pipe bolts to the exhaust manifold (after liberally soaking them in penetrating oil). Then cutting off the old muffler clamps in front of and behind the Cast. Then putting a thin block off wood between the exhaust and the cross member and tightening everything back up again with new heavy duty (a little thicker than stock) muffler clamps. I raise the exhaust a little higher than needed at the cross member, initially when tightening the new clamps, because it may sag a little from the weight after the new clamps are installed and/ sag a little after a few bumps while driving.

[yzmuddereffer]

Boy, you would think this would be simple...create rattle, listen for rattle.

Anyway, I think I'm narrowing this down to the exhaust. Inside the Jeep, the rattle sounds like it's coming from inside the front portion of the lower console. Under the Jeep, it's hard to pinpoint it, but it sounds like it's coming from the Transfer case... Unless you secure the rear driveshaft (e.g., hold it firm), then it sounds like the noise is coming from the muffler...

It sounds crazy but my current theory is it's moving from the muffler area of the exhaust to the rear drive shaft, though the transfer case then somehow resonating through the cavity under the console...

To test this I strapped the exhaust over to the passenger side tightly with a bungee. This morning (the noise is always worse when the Jeep is cold for some reason), there was no rattle at all on startup. This also might explain why sharp right turns immediately after startup prolong the rattling... maybe there was enough flex in the exhaust for it to rub the driveshaft?

What I don't understand, though, is how the driveshaft rubbing would magically go away when the Jeep warms up.

I didn't have time to test the hard right turn this morning before work, but I will tonight...

[heyhar]

We have two '96s, both have the busted cat innards. They broke, of course, after having the busted cat recall performed. They both rattle upon cold start-up, quiet down when up to temp, and rattle a little when the engine is shut off. Both threw a code, too, telling of an ineffective cat a few weeks after the rattling started. Both were cleared, and haven't returned.