i am getting a strange hissing noise from the area of the downpipe and i am thinking it may be my cat starting to go. No smells or anything else, but i feel some power loss. I want to replace the downpipe with something with a high flow cat, but my questions are will this cause me to fail emissions and will it pull a CEL? Also, should i get retuned for a header and dp? any help would be great

 

The hiss is an exhaust leak.

 

Thats what i thought at first, but the tech at the dealer said he couldnt hear it, could be my vibrant drowning it out! im gonna get it up on the lift wednesday and check the gasket between the header and downpipe and see if that might be it