I have a '07 Cayman and my dad has a brand new '09 Cayman. Both are base models. I drive mine most of the time with the radio turned off. I just listen to the sound of the engine and exhaust. I bought the car used, but nothin' was ever mentioned about any aftermarket parts on the car. I drove my dad's yesterday, and the first thing I did was turn off the radio, like I do mine. I was surprised when I couldn't hear anything but wind. There was no engine noise and no exhaust noise. I'm pretty sure my exhaust is stock. It still sounds pretty choked up if I rev it, and it doesn't sound like any of the aftermarket exhausts I've heard. The difference in sound is very noticeable between the two cars. His is so quiet, I decided to turn the radio back on, 'cause it sounds better than just the wind. What is causin' the difference in sound?