Hi Carl
Welcome to the forum.
Sorry to hear that you seem to have a similar engine noise to me, although it isstrangely reassuring (if that is the right phrase!) to know that others are experiencing the same.
As you have said elsewhere, the MPG does not seem to be as good as official figures (shocker!), but my dash read-out states 43.5mpg currently (still rising ever so slightly), after the car has done 11k miles (just under 10k in my 15 months of ownership).
Hope you enjoy your B-Max and the forum.
Wayne