Ok, so ive had a noise that appears to be coming from the area of the flexpipe on the downpipe. I do not know for sure bec when i get under it and check i find nothing. No cracks or anything, i even had my buddy cover the tail pipe and i heard no leaks. At normal idle it sounds fine, but when i accelerate, it sounds like a loud spitting and hissing sound. I let it go for a couple months figuring it would get worse if it was a problem and maybe then i could figure it out. Well, it did, now it also makes a loud ticking sound under throttle as well. I am hesitating taking it to the dealer because the car is not under warranty anymore. Does anyone have any suggestions. Im thinking a bad gasket or a crack that i cant see in the cat. Ill be pulling it off on wednesday to get a better look.

 

I'll be paying close attention to this one. I have the hahn exhaust and have hissing when under heavy acceleration. I already checked all the connections and everything seems tight. Might have to check the header again though.

 

Could be bad cat. I just had mine replaced under warranty. How is your boost? I have stage 2 and I had the hissing / whistling for a while then I started getting excessive boost I was hitting 20psi for a while then the cat became so plugged it would not even run.