Chevy & GMC Vans

I noticed yesterday while out with the wife that at times there is a rattling sound, maybe that is not the best description though, coming from the rear of the van. If sort of sounds like a loose heat shield or loose piece of metal vibrating against something else. It doesn't continue when we drive but ittermitantly comes up when we start from a stopped position. The only thing I have had sound like it before was when ice and snow have built up between the tail pipe and the body at the rear of the van and that ice chunk vibrates against either the van body or maybe it was the tail pipe. That is the best I can do to describe it. My question is where should I look for this. I figure check the spare is tight, look in the storage location where the jack and stuff are first, but what about other stuff under the van the the winter salt and snow could have rusted to cause this? Anything else mechanical? I am going to have to check the rear diff level anyway, so once I have it jacked up I can look for other things?

Although it could be a million different things it sounds like it could be your catelytic converter. When was the last time you had it changed?

Never thought of the cat. I have not had it changed as the van was very low mileage when I got it. I will give it a whack. I am pretty sure my thermostate is staying open, although I am not sure how long that has gone on. If I understand things correctly that would make the van run rich and would kill the cat.

Moved the trailer around today and heard it. It is definitely more to the middle front of the van and louder on the passengers side. I wish I had time to get under there.

If the trans or engine mounts get really worn, or the hangers fail, the exhaust can hit the trans crossmember. It is pretty obvious though that the pipe and crossmember are hitting when you look at it.

I would guess its the heat shield on the Cat. I had that problem on one of my old vans.

The first thing I would try is crawl under there and just start thumping the exhaust with your fist. Start with the cat, check for loose heat shields and hangars. Just make sure the exhaust is cool when you do this! Another thing to check, I'm not sure if your van is the same as mine here, but the oil fill tube and the transmission dipstick tube can both rattle if one of their brackets has cracked.

I'm going with the cat. The element gets loose and rattles something awful. It happened to the "Smilie Van". A new cat solved that.

I take it thumping the cat will tell me if the element is loose. Thanks for all the ideas.

Green has the same rattle coming from the cat.

So how hard is it to replace a cat on our vans. On my Suzuki it was all bolt in, on the Mazda it is welded although you could remove a rather large section of tail pipes and have it bolt in, that would be every costly though. Of course until I actually get under there I am only guess it is the cat based on the responses here.

If you buy it as part of the Y-pipe assembly (very common) it bolts right in. Otherwise cutting and welding is required.

Big price difference between direct fit and just purchasing a cat. I don't know if my welding is up to that, what do people recommend for a cat?

Since I can reach the cat without jacking up the van I gave it a thump with my rubber mallet. What should it sound like?

If the element is loose you should hear it rattle. I used a universal type cat and it was a weld in.

I think there is a rattle, but then again the rattle when driving doesn't happen all the time either. It comes and goes so maybe the stuff inside in not completely loose yet. When it does rattle is it very noisy. I will have to price out getting a new one installed. I might just go to an exhaust place and play dumb saying I have a noise there and see what they say. I am thinking the cat is the problem because the location is right and it sort of rattles when hit with the rubber mallet.