The Buzz About Dimmer Switches

Dimmer switches use a special circuit to pulse the power on and off very quickly. This pulsation causes the filament in the light bulbs to physically vibrate and make a high-pitched sound.

When the light bulbs are clearly the source of the noise, the solution is simple: change to a higher quality bulb with a heavier filament. This generally means replacing a plain ordinary type A bulb with a halogen bulb of a similar wattage. Halogen bulbs should have heavier filaments, which prevents them from vibrating when the power is pulsed.

Fluorescent bulbs don't have a filament, but you cannot use them unless you get a dimmer that is specifically designed for fluorescents.