From the spec thread:
http://f80.bimmerpost.com/forums/sho...d.php?t=923203
Quote:
•Electronically control Exhaust- ◦Electrically controlled flaps just before the rear silencer minimize exhaust back-pressure and produce a BMW M sound, as well as giving precise feedback on engine load
- ◦When closed, flow is forced into and laterally across the silencer; when open, flow is more directly through the narrow part of the silencer
- ◦Different selectable drive modes feature different engine sound profiles
- ◦Catalysts with metal substrate (less restrictive than ceramic)
- ◦Exhaust always exits all four tail pipes
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If it is controllable electronically, the sound could vary depends on what the flaps are doing. There is still much to find out.