Need help eliminating hum

Ok, I've got two sources of hum in my system and I'm not sure how to eliminate them. I'm running a Denon 3805 using the component switcher and two amps that power L/R/C/Sub. I have an HD Tivo running in to it, and the component output goes to my TV. The TV has cable running directly into it. So... component in from the HD Tivo, out to the TV. When the HD Tivo is on the line without the TV, I get hum. And vice versa. I disconnected the cable line from the TV and the hum is better, but not completely gone. So I've got hum coming from two sources, one of which gets marginally better when I disconnect my cable line. I will get an isolator for the cable, but that won't completely fix the problem. And i have no idea what to do about the Tivo.

All of the devices except the TV and plugged into a Panamax power unit, and outside the house both cable and sat lines are grounded to the main house ground. I tried the cheapo radio shack inline devices between the Denon and my amps, and it did nothing. Any other ideas?