i bought a dynomax catalytic convertor for my 2.8 and a dynomax cat-back also. I noticed, after about a week of driving, that at low rpm's, 700 to 1300, a weird noise, a rattling noise, was coming from my catalytc convertor. I have no idea what it is, maybe a bad catalytic convertor or something. Ive had the catalytic convertor on since the beginning of april and was hoping the noise would away. Has anybody ever had this problem and have they found a way to fix it??????

 

It's the heat shield on the CC is loose, broken, etc.
ALSO check the tranny mount for the CC brackets, too.

 

its not the heat sheild, but ill check the tranny.

 

Check the clearance between the hanger at the rear of the catalytic exhaust and the car. It's possible that (a) the hanger loosened up from the cat flange or (b) the hanger is banging against the exhaust pipe.

 

If the rattling is coming from the converter itself it is more than likely a loose "core" inside(the thing that does the converting). It is wrapped in a fiberglass mat to hold it in the body. It is burnt out and the only thing you can do is replace it before it drives you crazy!