H20, as in DirectTV reciever?

I don't have one, but if I have just one component connected to the 990, it still does it.

Take your pick, they will all result in the same conclusion:

SA 8300HD
XBOX 360
Denon 3910

Again, to test you need a signal, and to get a signal, you need at least on component connected... All of the above are connected via TOSLINK only.

Even disconnected the cable from the 990 to the TV (to see the setup menu), and no change.

If it is a ground loop caused by product, I've just about eliminated all hum using the common ground (no cheater plugs).

Whatever it is, I wish it was either more common, or more forgiving. Other than that, the 990 works out well for me using the balanced connections.