A while ago I was getting a humming sound from the right front of the car when making high speed left turns. Some people suggested bad wheel bearing. That seem reasonable.
It turns out I had switched to 535i solid engine mounts and both of them were cracked from driving on the street. One actually had snapped in half. I recall others has similar symptoms, so fellow enthusiasts may want to check the engine mounts. Mine were only 1 year old. Now I'm back to the original mounts, much smoother and no humming.