I noticed today when I was accelterating that there was a nasty rattling sound and it sounded like it was coming from the underside of the car. I have dual catbacks with headers in the front so the cats are right under the driver and passenger. When you rev the engine the cat on the left under the driver makes a nasty rattling noise. I thought i saw smoke for a minute but that could have been heat waves. Is it possible that the cat is busted internally or something? It's either that or the pipe on that side of the car is severely hitting the chassis right where the cat is. Help guys. Very discouraged today. Some bitch *** left 4 scratches on the side of my car and a crack in the side, but of course there is no note. The body shop is apparently closed on saturdays too. Oh yea my alternator is broken too. And the clip that holds the panel of window buttons and door lock buttons has come off so my panel just kinda hangs out of my door. Some bitches are really inconsiderate.

 

A rattling in an exhaust can be anything. Hack or pull your CAT off and take a look. The pieces inside the CAT can come lose and rattle. I would check your entire exhaust. A friendly exhaust shop will let you put it up on your lift and have some rev it to hear exactly where or what is happening.