Several things can make a ceiling fan hum. In many cases, imbalanced blades cause the noise. The noise could be from the motor itself. Troubleshooting can help determine the cause of the humming noise. Once the source of the noise has been identified, the fan can be repaired, often as a do-it-yourself job.
Grab the fan blades to see if they feel loose. A loose blade can lead to a noisy fan. Tighten the screws that hold the blades with a screwdriver.
Measure the distance from each blade to the ceiling, using a tape measure. Blades that aren't lined up with the others can cause a humming noise. Carefully bend back any blades that need to be lowered to be in line with the other blades.
Apply fan motor oil to the motor unit. Follow the instructions on the can.
Tighten the nut that holds the diffuser in, using a wrench. If this nut becomes loose, the entire fan could rattle, leading to noise.
Inspect the light bulbs in the unit, if equipped. A loose bulb can vibrate, causing the humming noise. Tighten the bulbs into the sockets. Gently move the light bulb sockets around so they do not bump into other parts of the unit.