Is there a coax line going into any of your equip?
The only coax is to the setup box connected to the AVR via HDMI. No hint of any noise/hum whatsoever.
Is there a coax line going into the HTPC?
Is your cable/sat coax grounded at your home's fuse panel?
Since I never noticed any kind of noise/hum/interference, I'm assuming it is properly grounded.
Is your "clean power" on the same wall outlet as your AVR, Tv, etc?
Yes but there an APC UPS between the wall outlet and the HTPC.
Can you plug everything- HTPC, AVR, Tv, etc into that clean power device?
I'm not sure it'll be able to handle the load when there is a power outage but for the sake of testing, I will try that out once.
Does the clean power device have coax in/out?