I used to have an rattling issue with my Greddy Evo II exhaust rattling against the frame. I've found several people with the same issue. If it's against the gas tank I can't help u. But if it's where the pipe archs up all you have to do is bend the metal hanger piece attatched to the car. Bend it downwards that is. you can do this two ways, one is you can get a short pry bar (a long one won't fit in the wheel well) and force it down. Another way is if you have a cutting torch, heat the hanger (DO NOT cut it, AND POINT TOWARD THE SIDE OF THE CAR UNLESS YOU WANT TO HEAT UP YOUR GAS TANK) when it is red hot use pliers and gently pull down. I would suggest using lower pressure on the torch so the flame will be shorter and not hitting your gas tank and brake line. Problem solved.