Shorty mate, if your talking about the standard 172 exhaust, the best thing you can do is bin it, save your pennies and get yourself a decent K-Tec or Magnex CAT back. What you describe sounds like the stanadrd system baffle problem (4K rattle). The after market systems sound much better (as Reno should have done standard) and get rid of all your rattles/buzzes and tinging noises. I have the Magnex which sounds nice and reasonably quiet. Drove my mates Cup with a twin pipe K-Tec this afternoon. Its a bit louder at lower revs but sounds awsome when you give it some beans. Neil