I know this thread belongs more to the exhaust forum, but since this is the most visited between all sub-forums, just wanted to share the experience with you
Yesterday I did a small mod to the 2 vacuum valves on each one of the inner exhausts of the X6M, now all 4 exhaust tips remains open at all times ( when stock the 2 inner valves don't open until the car reaches some speed about 3000 RPM's)
The result is a real low frequency "V8 sound" when you start the car and drive at very low RPM's, is more like a "subwoofer sound" nothing loud.
Here some links to YouTube videos I made before and after the modification, also a couple of pics for better understanding. I'm VERY satisfied with the new sound results. Now my car sounds like it has BIG-balls......sound from video does not make justice, was taken with my iPhone.
Before and after videos here:
Before:
After: