Wall Switches Hum
My wall switches are installed and appear to be working properly, but they emit an audible hum. Why does this happen? Is this normal?
It is normal, but it can be bulb dependent - some types and sizes of bulb might hum more than others. Dimming can also amplify the humming. You could try a different type of lamp (note though that ONLY incandescent lamps can be used with most dimmers). You could also check to make sure the wall switch is firmly screwed in place, to make sure the humming isn't being amplified by the switch vibrating against the wall box. Also make sure the wall plate is securely screwed in place.
Bulbs sold as "rough service" bulbs may hum less- see this article for more information: