humming when dimming panel lights

[dado]

2004 Outback Sport
I still have the original audio (no comments) but I'm thinking about an upgrade.
But before I go about that, I wanted to find the source of a little problem.
When I dim the panel lights, a medium pitch hum comes on through the stereo.
Has anyone seen that before, or know what it could be? It seems to be a grounding problem, but that's how far I go.
I wonder if just replacing the head unit will get rid of it.
One guy at the dealer said it was normal, that some of the cars have it and there was nothing he could do. Can you believe that?

My warranty is about to expire.
Should I make a fus and have them fix it?

Thanks.

[dado]

I thought I was on the subaru owners forum.
Sorry for the cross post.

[exalted512]

just because it happens to a lot of cars doesnt mean it should be there, you are getting some type of electrical interference somewhere--if it bothers you id have em fix it if its under warranty
-Cody