I have a metalic 'rattle' in the exhaust system, usually at idle and low rpm under load. It's worse when the car is cold. At first I thought it was the heat shield because the clamp was rusted and the shield was loose. I secured the heat shield but the rattle remains. When I 'hit' the exhaust system with my hand I can hear the rattle but I can't figure out where it's coming from. It sounds the same whether I tap on the 2nd cat, the resonator or the muffler. It appears to be a loose baffle. I'd rather not replace the entire exhaust if I don't have to. Does anyone have any experience with this? Which component is the most likely culprit? Thanks for your help.

 

I had something similar I roll a 2003 Mazda. After some searching, it was concluded (by my mechanic) that it WASN'T the exhaust. It was an Hydrolic Valve Lifter. It makes a ton of a racket when it's cold and after a while levels off. That's my 2 cents anyway.