My car started to make a rattling noise like a month ago, so I finally decided to get it checked out at my local honda dealership (some portions are still under warranty, BTW its a 2000 civic SiR) The mechanic told me that my center pipe was rotting from the inside, and that the rattling noise was the inner pipe found inside the center pipe vibrating against the outer half. Is it possible that this sort of deterioration could negatively affect my performance? My car is mostly stock.

 

the cat was coming apart? i'm not getting what he means by a rotting center pipe...

 

Within the stock center pipe there is an inner pipe. The inner pipe is starting to deteriorate and is thus hitting against the outer pipe.

(o) <------- i.e.) the "o" is hitting against the brackets.