When a switch begins to buzz audibly, it means that the current between the metal wire contacts inside the switch is arcing—jumping the gap between metal parts rather than flowing continuously through metal pathways. This causes the crackling sound, and it can lead to burned contacts and heating of the switch and the wiring connected to it—all problems that have the potential for causing a fire. So whenever you hear a buzzing switch, you should view the symptom seriously and take actions to diagnose and correct the problem or replace the switch if it is faulty.
Some dimmer switches have different operating mechanisms, using a variable rheostat in which it is perfectly normal for the switch to make a very slight humming noise when the switch is moderating the electrical current to dim down the light intensity. If a dimmer switch makes this slight humming sound when the light is on, it might indicate a problem, but don't leap to the conclusion that the switch needs replacing. Look at diagnosing it first.
Before You Begin
People routinely remove cover plates on a switch without shutting off the power, but this is bad practice, and it has more than once led to a homeowner getting a nasty shock—especially in situations where wire connections are loose. Always shut off the power to a switch or other electrical fixture before examining the wiring.
Equipment / Tools
- Dimmer Switch
Open up the Switch
Shut off the power to the switch. Carefully remove the cover plate on the switch. You may need to loosen the mounting screws on the switch and slightly pull the switch forward out of the wall box to see the metal screw terminals.
Check for Loose Wires
Examine the screw terminals along the sides of the switch to make sure they are securely fastened down over the circuit wires.
Tighten the Screw Terminals
Gently tighten the screw terminals to make sure they are secure. Put the dimmer switch back into the wall. Cover it up with the switch plate, then turn the power back on.
Plan on Replacement
If the switch continues to buzz after you have tightened the screw terminals, it likely means the switch is faulty and should be replaced.