I own a 05 Civic SI and just recently installed a greddy exhaust evo2. I notice that when I shift gears or when I decelerate I hear a popping noise from under the passenger seat. Is there a leak in the piping? Does it need to be tightend or welded on? Or does it require a heat wrap to cancel out the noise?

 

dont quote me on this but i think its just because the piping is bigger, and ur muffler not as quit, so when u get off the gas all the compressed air comes out a lot faster then stock, causing that popping noise

 

that could be the problem but i would tighten it to be sure aswell