Mac Mini- HDMI audio noise problem

When I hook my Mac Mini up to a Panasonic HDTV, the picture is fine, but I get some pretty bad audio noise. It changes/increases when I open up files, apps, etc. It sounds like it's amplifying the noise inside the computer. It stays the same regardless of whether I change the volume on the TV. Even muted, it stays the same. I don't have this problem with the audio out, just with HDMI.

Any ideas?

thanks.