This is an interesting
problem. I have experienced it myself, but I heard the sound
from the light bulbs more than the dimmer switch.
Apparently what happens is
the dimmer switch uses 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
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. Supposedly halogen bulbs
have heavier filaments and they don't vibrate when the power
Also, Rough Service bulbs
(the kind used in trouble lights) may have a heavier filament
and make less noise.
Fluorescent bulbs don't have
a filament, but you cannot use them unless you get a dimmer
that is specifically designed for fluorescents.
If changing the bulb type
doesn't solve the noise problem, then the next thing to try would
be replacing the dimmer switch.
Bruce W. Maki, Editor.