The aftermarket air deflectors cure this problem nicely!
EVERY car/truck/suv I have ever owned that had a sunroof had that wind buffeting problem!
I will contend that the ML seems to be worse than the others. But I bought an aftermarket air deflector and it not only cured the buffeting, but reduced wind noise considerably!
I can actually maintain a normal conversation at 65 mph with the sunroof open without yelling!