I need some help...
 

NEED HELP: I recently added Fast Intentions exhaust with 12" resonators to my 370Z along with installing the Stillen Gen 3 and everything sounded fine. It was certainly a deeper sound in the cab and all of that, but it sounded good to me without any rattles etc.

Today, I had my test pipes installed, and now there is a hissing/rattle sound that's primarily on the down rev side. Sometimes on a hard up rev I can hear it but it is consistent on the down rev side. It's like the sound is from inside the exhaust, not like something rattling on the outside such as an exhaust hanger and such. It almost sounds to me like there's a piece of metal or something inside the exhaust that's causing the hiss/rattle. Any ideas what it may be?

Thanks for your help in advance!

The VQ hiss is normal and is amplified withe the gen 3 and FI. This occurs on deceleration wheather under load or not. A rattle is something you will have to narrow down. Loose heat sheild or something similar possibly.

Are the test pipes hollow or high flow cats? If hfc it could be something loose inside. Chances are you just need to get back under there and have someone rev it up so you can pin point where it is coming from.. Can't wait to hear it man!!!

Thanks for the replies. I want to add that I never heard anything like this with the Gen 3 and Fast Intentions fatback installed. I only heard this once the cats were removed and test pipes installed. They are straight test pipes with no resonators and they are hfc. The only resonators I have are the 12" resonators on midsection.

:iagree:

Hiss is status quo when you remove factory cats. Kind of like the flywheel chatters a lot. Normal for the platform.

You may wanna check if all the gaskets are on right and there aren't any leaks. Other than that you're good. Test pipes tend to make the car hiss. FI exhaust has a hiss to it. Add test pipes and you got yourself a hissing machine that sounds glorious ;)