I have an HKS hi-power cat back on my EK hatch. The canister is dented pretty good in the rear (not even noticeable when on the car). Well there is no major hole but enough so that at idle i can feel air coming out the rear. Could this be making my exhaust sound louder?

 

USUALLY any holes in the exhaust will make it louder... (the hole is an easier path for gases to escape)

it'll be louder esp the more you get on it...