I am hearing some wired Rattling noise at first i thought it was coming from the pipping heat shields at bottom of car. Not those, and now i KNOW its comming from under the hood somewhere i checked the Short ram, is secure, i checked under the car, and made sure header was secure what else could it be? Could it just be that my Exhaust pipping on my system is to small 1.91 inches (stock i am about to get new system tommrow 2.25) any help would be great thanks guys.

Oh ya its a Greddy header if anyone needs to know, and i reused my Orignal Gasket (It looked fine)

 

well, had you used a new header gasket (like recomended) then that would be ruled out. Sounds like you diagnosed your problem

 

Got it, pipping to small and created backpressure and made rattling now its good.

 

Wow it was also where the front of the cat converder is where bottom part os header and cat converder meets was ratteling really bad...