I recently installed a ceiling fan and when I turned it on a fairly loud "motor" hum happened, especially in the lower speeds. Thinking it was a cheap fan I bought a second fan which does nearly the same thing. A salesperson sounded very surprised that the first fan hummed, and I listened to the second fan at the store and it sounded fine. The hum has nothing to do with rotation either because it starts immediately when the fan is turned on. Does this sound like an electrical problem? help.