My ceiling fan makes a peculiar humming noise. It makes me think about how the fan is spinning at some frequency and causing vibrations in the blades. Perhaps the vibrations of the blades are resonating. Or perhaps the humming noise is simply from the lights on the fan.
I'm not sure but it may be spinning at approximately 70cylces/30sec (~14Hz). My eyes feel weird now. Counting spinning blades is trickier than I imagined.