Just a quick thanks for this sticky. Two days ago I got a Vizio LCD and an Onkyo SR605 to go with my Time Warner Samsung HD box. Well, I can't figure out a solution to the HDCP problem that's keeping me from running the cable HDMI through the Onkyo, but I can run it into the TV and run digital audio (coax) into the Onkyo. The Onkyo has an HDMI running into the TV also, for the DVD and other stuff.
So, that three-way dance caused a hum. After getting down to the bare minimum config and still having the hum, I called Onkyo and spent 40 minutes resetting everything and undoing all the speaker wires, and finally having the guy tell me to exchange it where I bought it. Hey, that thing weights 20 pounds easy and is one PITA to return. Plus, I really didn't think it was bad.
Then I looked here and read the sticky. Oh. Well, I still don't really know what the problem is, though I see lots of things to try, like post 64. Still, the critical thing for me so far was reading that optical doesn't cause this problem. I switched the box > onkyo from coax to optical and there went the problem. Happy happy joy joy. I'll look into the other stuff, but at least I can sleep tonight without cursing.