APR S3 Catback Exhaust. The vehicle is driven in various configurations (with the factory DP and the APR Race DP) in drive and sport mode. All valve functions are left in their stock operating mode, which is closed while revving, and changes during light throttle in drive mode. We've also installed our optional "exhaust crackle" tune which can be heard during free revving and lifting off the throttle with the race DP installed. This feature is optional.