Beernut,
Simply replace the dimmer with a higher quality unit from Lowes or Home Depot. Chances are the dimmer was installed orginial construction on your home and is probably the cheapest thing on the shelf the builder could find.
Go with a high quality Lutron dimmer. I use one in my dedicated listen room mainly for mood lightly and I get ZERO hum with my Cary SLI-80. Dead Quiet.
I posted the link to the dimmer used in my listening room below for you.
http://www.lutron.com/faedra/?s=17000&t=17200
Good Luck!
Chris