Scott,

I had a hum on my 990 once I started to use it as a dvi switcher. This thread is where it was discussed. Basically my hum was coming from two locations, the sat/coax in to my HD tivo, and the ceiling mounted projector being plugged into a different outlet than the rest of my equipment. The hum came back about a month or two ago but only on the center and surrounds when using the analogs of my hd-a1. I traced it to the power adapter for the 7" b&w tv I put in my rack so I could see the 990 setup menus and the tivo screen without turning on the projector. The power adapter dropped a bit, and was sitting on top of the analog cables for the surrounds and center going from the hd-a1 to the 990. Hope this helps some.

John