this happend to my brothers gsr first do you have the stock headder? second if the dohnut gasket between the headder and cat is worn or somthing the pipes will bang. The springs help the exhaust system flex a little bit putting less pressure on the actual header where it joins the head. Back to the stock headder there is what an acura mechanic explined a b-pipe inside the actual stock headder and on my bros car it rusted away and just rattled. All he did was replace the headder and the banging went away.