Why is the ford focus making a humming noise when accelerating?

The most common reasons Your Ford Focus would hum when accelerating have to do with the wheels and axles. The top cause is likely a failing wheel bearing, but You may also have issues with Your CV axles. It's really difficult to say though, since an alternator issue may manifeSTSimilar symptoms. Have Your checked for diagnostic codes yet It's possible that Your Focus is telling You what's wrong with it; You just need to listen. The best thing to do if not is try to isolate the sound; is it coming from the right or left Front or rear You can jack the car up and see if any of the wheels have "give" -- this can indicate issues with wheel bearings or ball joints, both of which can cause humming while accelerating.