My 98 gsr had a high flow cat put on the other day by a muffler shop. Also have greddy evo2 cat back exhaust. Anyways, i was wondering if anyone else expected a different sound to come from it. It almost sounds as if it is rattling. I can hear it right under me when driving. I expected my exhaust to be louder which it is, but the rattling noise im not too fond of.

 

If they installed it correctly, there should be no rattle whatsoever. Either something is loose or your missing a gasket.Take it back and tell them to fix the rattle. Stock, high-flow, or test pipe, there should be no rattle.

If they can't fix it, you need to go to a better quality muffler shop.

 

Take it to the muffler shop again.....it's rattling against something. There shouldn't be a rattle.

 

it can also be that they didnt tighten the 02 sensors tight enough and its rattling and leaking exhaust.

happened to my car