Hey everyone, my wife has a 99 blazer 4dr. 4x4 with 135k on the clock.My problem is every time the compressor cycles, the exaust rattles bad. I crawlled under and it sounds like its comming from the cat. My question is could something in the cat break loose and rattle? Thanks for any help.

 

Absolutely. The honeycomb of metals in the cat can burn out and break up causing a rattle. If the cat is not replaced, the pieces can move to the muffler and plug it, also. A plugged exhaust will have a negative impact on performance.

 

also, u may want to go under there with a rubber mallet and just tap the cat a few times to see if u can duplicate the sound. Also bang the floorboards a few times and see if u can locate the rattle, U might find that the problem is something like a rusted out heat shield. Im not sure how many heat shields are under there, as ive never paid too much attention to them, but i know for sure that there is a big one running down the side of the gas tank.