Thanks Tony. That makes sense. I wonder, then, why the incandescent bulbs in my bathroom vanity also make that buzzing sound. They are also dimmed, but the buzzing comes from the fixtures and not from the switch. Is that still the dimmer producing that buzz?

If that's so, I wonder why all sorts of combinations in the rest of my house don't have this problem. I have LEDs and incandescents on dimmers and lamp modules elsewhere and they don't make this noise...