Electrical – Buzzing sounds when I switch off the electrical socket

Why do the bulbs buzz when dimmed?

When you pass AC current through the filament of an incandescent bulb, it produces a magnetic field. This magnetic field tends to push against itself, so there's some mechanical force acting on the filament itself which causes it to vibrate slightly. When running at full power, the AC is fairly close to a sine wave (either 50Hz or 60Hz, depending on where you are) so this vibration is pretty much constant and generally barely noticeable.

A dimmer will truncate and clip part of that sine wave; this introduces a lot of higher-order harmonics, which in turn changes the characteristics of the magnetic field, changing the way the filament vibrates. Depending on how the filament is supported, this may cause resonance at certain dimmer settings, leading to the vibration becoming noticeable.

See this article for some more background information on how dimmers work, including a mention of this phenomenon.

Are there other bulbs that don't buzz when they're dimmed?

If you prefer incandescent lights, look for rough service bulbs; the filament and its supports are designed to withstand more vibration than normal bulbs. You could also try halogen bulbs or even dimmable CFLs.

There are a couple of possibilities: the most likely is that the switch is worn and should be replaced. If the switch makes a good connection sometimes and a bad connection at other times, you would hear the noise only occasionally.

If your local laws allow you to do the work yourself, I think this would be an easy task. The steps would be (at least in the US where I am):

1. turn off the circuit breaker;
2. remove the switch cover plate;
3. double-check that there's no voltage at the switch in both on and off positions;
4. unscrew the wires from the switch
5. screw the wires onto the new switch
6. reinstall the new switch and cover plate.

Another possibility, but much less likely, is that there's a loose connection between the switch and one of the wires. The steps to fix this would be the same as for replacing the switch, but tighten the screws on the wires instead of removing the wires.