I recently replaced my stock cat-back system with the following:
B-Pipe from AutoZone
Stock Muffler

The Y-Pipe and cat system is from warpspeed and has been on the car for about a year.

The noise I am hearing is coming from the B-Pipe contacting the heat shield around the old factory B-Pipe, and hitting against the bottom of the car. It appears to be directly under the rear seats. Any suggestions on how to fix this?
1) Replacing the heat shield doesn't seem wise.
2) I was told to bend the heat shield against the car so that it would not hit against the bottom (Firestone advice).
3) Options.

 

Remove the factory heat shield

 

Get rid of the heat shield. If you are then worried about the heat, get exaust tape. You really dont need the heat shield.

 

Lose the heat shield and wrap the pipe with exhaust tape. I did it about 6 months ago and have had no problems.