I have installed 4 ceiling fans (2 Hampton Bay and 2 Hunter) and experienced the same thing. A humming sound from the motors on all of them. I used 12G wiring and spliced into 12G existing wiring in the attic. The mfrs don't understand why - one has asked if I have enough power going to them. If not, the motor may be struggling and, thus, the humming sound eminating from the motor. Other than the humming, all work just fine. Any suggestions?

Read this and tell me if it helps:

General ceiling fan troubleshooting and help FAQ- Ceiling Fans N More (http://www.ceiling-fans-n-more.com/ceiling-fan-general-troubleshooting-and-FAQ.php#6)

If the link doesn't automatically take you there, scroll down to part VI