There isn't an exhaust flap as such but there must be something in the engine map that allows some crackles and pops in sport mode. The car doesn't revert to comfort either if you turn it off in sport mode but the DSG does revert to comfort drive mode. Also weirdly you have to reengage sport mode in the driving modes to get the pops and not just flick the lozenge to sport (if that makes sense?)