I own an Apex'i WS2 and its quiet, but definitely louder then stock. Took the 101 to Chumash this past weekend and let me tell you, you start to notice it over a long drive. I could definitely tell the difference when I installed the exhaust, but an even bigger improvement when I added my Injen CAI. You gotta eat before you can poop right... so get both. Next step its headers.