Here is what I would do as I went through this about 30,000 miles ago thinking the worse that my front differential was toast......but it wasn't.
I ended up changing both front wheel bearings...funny thing is the side I thought was making the noise was actually the opposite side. I originally thought it was the drivers side front bearing as that is where the noise seemed to be coming.
Then I thought it may be the front differential as it is on the drivers side and looked to be leaking. Put in fresh oil, thicker and noise still there.....then panic set in as there were only 2 used front diffs in the country, or spend $2000 on a new one.
Finally, my neighbor got my car up on his lift and we determined the front passenger wheel bearing was making some noise, but that didn't cure the problem........ended up finding the fron KW V1 struts were shot on the drivers side....absolutely toast.
Put new struts on and the Humming noise went away! Must be the struts dampen the noises from the wheels and road...basically with a blown strut I had all the vibrations and noises go from the wheel right up through the steering wheel.
2008 335xi - 6MT - BMS JB4 G5i - BMS DCI - BMS OCC - BMS WW Meth - Spec Stage 2+ - Spec SMFW - 19" MVR Magnum's - KW V1's - TMS 12.5+20mm Spacers