Are the lights just low voltage halogens? Or are they compact fluourecents?
Low voltage lights have transformers, and these can hum. I suppose that could be reflected back to the switch.
As for dimmers, you have to add up the total watts and get a dimmer rated to handle at least that much. Remember that most fluorescents cannot be dimmed at all, and those that can, the dimmer must also be rated for that type of ballast. Some dimmers are not.