Bulb Failure
A single popping sound followed by a bulb that suddenly goes out can only mean one thing: your light bulb has failed. This can occur with both incandescent and fluorescent lights. Incandescent bulbs often "pop" when you first turn power onto an aged filament as it burns out. Fluorescent bulbs burn out when their voltage adapter mechanisms stop working correctly. Replace the bulb and solve the problem.
Wiring and Switches
If the bulbs do not appear burnt out and the popping sound is a re-occurring issue, it could be caused by faulty switches or wiring. Even though you cannot see the wiring in the walls, it can develop frayed insulation and eventually short out or fail intermittently. A popping sound from the walls may be your only clue -- and also can cause in-wall fires. Call an electrician to locate and fix the wiring problem before it becomes more serious.
Panel Connection Failure
Sometimes the connections within your fan are faulty, causing electricity to arc and disrupt operation while making a popping or crackling sound. This problem may occur within the fan or outside the electrical panel instead of within the walls, making it easier to see or smell. You must replace the electrical panel in order to restore operation to your fan lights. This is a job for a professional electrician, so do not attempt it yourself without the necessary training.
Blade Issues
Fan blades can also become bent and warped over time. If the popping sound is continual and timed with the revolution of the fan, it could be caused by a warped blade that moves incorrectly and clicks against the framework with every turn. Check your fan for any obvious signs of damage and adjust the fan blades to ensure they are within the correct framework.