I've got a 2002 with the v-6 engine. Does anyone else have this problem:
When the truck is idling in the driveway or coming to a stop at in traffic, at around 1800 rpm I get a very loud ringing sound. I have chased it to somewhere near the cats, but when I climb around under the truck there is nothing loose. It sounds like a heat shield or some bracket vibrating, but I have no idea what or where. Anyone got any ideas?

 

There's an exhaust hanger at the rear of the transmission, holding the crossover pipe. Check the bolts holding that bracket to the tranny. The bolts may seem tight, but make sure there is NO movement in the bracket.

I had to apply some heat to mine to tighten them. Watch the fuel lines above the tailshaft.....

 

Also check the black mounting brackets on each side of the engine near the exhaust manifolds. The factory uses these brackets to lower the engine into the engine bay. Mine had a loose bracket on the passengers side that was rattling up against the exhaust manifold bolt when the engine was at about 1500-1800 rpm. It only done it at that rpm. But anyways, if this is your problem just bend the brackets outward away from the exhaust manifolds. They are flimsy and bend easily so don't worry about breaking anything. Hope you find the problem.

 

I forgot to tell you if the bolt that holds the bracket in place is loose, use a 1/2" socket or wrench to tighten it up. I think that's the size.

 

Could it be that the catalytic converter material is breaking apart and rattling inside the housing. my girlfriends 96 jeep does this, but ironically it has not thrown a code to the computer. it only rattles when the engine is cold. once up to operating temp then the cat usually stops rattling. also note that with hers, it only rattles when the car is at idle speed, as soon as the rpms go up, the flow through the cat makes the rattle go away.



just my 2 cents...... hope that it helps

curt