Stumbled across this on BMW.com. If you click on "Drivetrain" then the "335i M Performance Exhaust" and then use the little arrow button to advance past the first two images, the 3rd will play a recording of the M Performance exhaust revving and then driving away, the 4th plays a recording of the standard exhaust. Link below:
http://www.bmw.com/com/en/owners/acc...ies_sedan.html