You should not hear a lot of noise.
My 320D M-Sport has slightly more road noise, depending on the road surface, compared with my previous 320i SE.
I put this down to the larger tyre sizes on the M-Sport.
But given a good road surface, on some of our motorways and most/all French motorways, it can be very quite indeed.
PS Perhaps there could be a little more cabin noise in the M-Sport due to it's diesel engine.
PPS I would not be going back to a petrol BMW
