M3Bliss: I can't find any posts in your link.
The noise is not heard inside the car when the windows are up. Only when down you can hear it coming from under but not sure whether it's the front or the back of the car.
I will replicate it on the way to work and list the exact sequence of events. Thanks for the input so far.
E92 M3 2007 - ///PE with Test Pipes and BPM Stage II; CF Interior & Splitters; CIC with Connected Drive