Stock exhaust piping, Omptimized Y pipe and a Magnaflow high flow cat will produce a louder exhaust,
beacuse more air is going through the exhaust system.
Also it's possible that one of the welds didn't get sealed properly.
1996 2.5LT V6 Contour ATX
My Tour+help/info pics
E0 rims, Gutted Pre-Cats,CTA Custom Exhaust & Intake, Diablo Chip.