Hey all, I have a 99 Ram 1500, 5.9 360.

Runs great except for one tiny problem that's driving me nuts, There is this "Rattle" coming from under the truck somewhere between the cab and underneath the engine.

I don't believe its engine ping or knock, because I cannot hear it at all when standing over the engine with the hood up, only when I get out of the drivers side door can I really hear it. It doesent have a "Rhythm" either like engine knock usually does, Its a very Random sound, it sounds like something is just vibrating against something else.

It does not happen when the trucks cold, only after its warmed up to operating temp.

Anyone ever heard of something similar? I'm pulling my hair out trying to find the cause.

Any help would be super apreciated!

Rap on your cat converter when it is cold, see if that's it.

You mean like shake it or hit it with something?

Smack the cat with a rubber mallet. If it rattles, it's bad.

Well I checked it, and you were bang on, with the truck running I crawled under and the sound is undoubtedly coming from the cat...So thanks for the help, but at the same time now the Mechanic is gonna rape me, I hear those are expensive to replace

On your cat, do you have a single pipe going in and a single coming out the back, or do you have dual pipes going in?

If single pipe in/out, not to expensive at all. Even if you get it at a the mechanic, like I did, I paid $400 for new converter, new muffler, and all labor. Magnaflow High Flow converters are cheaper than factory units, and flow better.

Nope 2 pipes in, one pipe out....More expensive I assume?

Should I even be driving the truck with the cat in that condition? Can I further damage something? I do not have a CEL on.

Do you have emissions testing/inspection in your area? If not, just disconnect the pipe behind the cat, remove the pre-cat O2 sensor, and knock the crap out of the substrate in the cat...... pull out what you can, start the engine, and blow out the rest. Put the pipe back together, reinstall the O2 sensor, and don't worry about it.

Forgive my lack of knowledge, but by substrate, you mean the honeycomb mesh **** inside the cat right? Stick a pipe or something in there, smash it all to hell?

No, I do not have emission testing here.

Exactly.

Reason I tell ya to remove the pre-cat O2, is so ya don't whack it when cleaning the cat.