Similar sound heard at steady speeds between 135 to 145 km/h in my A45S. As soon as pressure in the accelerator pedal is increased or decreased, sound stops. MB claims all A45Ss do it. To me it is not normal.Thanks for the reply. Yea I'm hoping its not the turbo really, even though it is covered under warranty still! Its not there when the engine is cold and seems to get a little louder as the engine heats up. Its not loud but it's definitely annoying!