yer dude i had the same problem hey u can use all plastic polishes and shit but all i used was some tooth paste polish it in then leave it 4 a bit and rub it off wit a damp cloth. cheep and effective!
I got a x-force 3.5 inch catback on my 33 gtst sound sick real burbly on backoff not to loud at idle just wen u hit it it roars! nice sounding exhaust system