Well now that my BW 45 has arrived (mirrors now fold/unfold on locking/unlocking), it appears that I have the Sound Actuator fitted.
With the mode in 'Normal', engine just sounds like you'd expect, but in 'Sport' the engine noise is much deeper, louder witha bit more of a growl. Definitely a different sound between the 2 modes, managed to find a back road where I was able to try the modes back to back and accelerate (mainly in 2nd). Tried it lots just to make sure of the difference too