Tighten the screw in wall mount that mounts it to the wall. It might look tight but its loose. The wall mount is vibrating on the wall as the internal unit spins. I had the same sound and it wasn't until I moved everything to another room and remounted everything that I realized the cause of the vibration. When i went to remove the light house it was a little loose against the wall. I then noticed the problem again when I remounted everything and tightened the screw and the sound ceased immediately.