A dimmer switch can help create ambience by allowing you to get your lighting level just right. Or it can destroy ambiance by making it sound as if your chandelier doubles as a boarding house for cicadas. This buzzing noise is a common unintended consequence of dimmer switches, but it's not a necessary consequence. If you need help making sure the effects of a dimmer switch are seen, but not heard, here are a few possible solutions.
It's a common, and understandable, misconception that dimmer switches simply reduce the voltage of the electricity that goes to a light fixture. In fact, the voltage doesn't change. Instead, the dimmer cycles the electricity on and off very rapidly, far faster than the human eye can follow. So while what's really happening is that the lights are turning on and off, your brain interprets it as the light being dimmer. This rapid cycling can cause the filaments of your light bulb to vibrate, and it's this vibration that creates the buzzing sound.
If your dimmer switch is operating near or even over its capacity, it won't operate as smoothly and buzzing is more likely. You can reduce the load on the dimmer by reducing the wattage of the light bulbs it controls. Because this is the least expensive potential solution, it's a good idea to try it first.
If lower wattage light bulbs don't solve the problem, try higher voltage bulbs. Standard light bulbs are 120 volts. But 130-volt light bulbs are also available and could be the solution to your buzzing problem. These bulbs have thicker filaments and heavier housing, so they are less prone to vibration. If you're having trouble finding them, look for light bulbs that are marketed as "long lasting," "rough/heavy duty," or "outdoor." Specialty appliance and garage door opener bulbs are also typically 130 volts. And if the lower watt bulbs you installed solve the buzzing problem, but you find that they burn out frequently, replacing them with 130-volt bulbs solves that problem as well.
If changing your light bulbs (twice!) doesn't solve the problem, then the culprit may be a cheap dimmer switch. Switching a light rapidly on and off is an inherently unsmooth way of powering it, but higher end dimmer switches generally accomplish the task more smoothly than less expensive dimmers. They also include components that minimize fluctuations of current that the on/off cycling can produce. These higher quality dimmers also generally offer a broader range of settings, which gives you greater control over how much or how little your lights are dimmed.