Solved! Go to Solution.
Actually, I think I found the solution. The STB (DVR) has an "Audio" option on the menu that allows the user to control how much power is emitted from the STB to the TV and whether the STB will control the volume or the TV will control the volume. After changing the settings (combined) the hum was eliminated. I will continue to monitor this from channel to channel to see if this is consistent.
I think I chose the following: 1) Let the STB to control the volume; 2) Select volume type is "Surround" & Stereo, since I have a surround sound TV feeding into my sound system; 3) Volume is "variable"; and finally increased the overall volume emitted from the STB instead of "fixed" at a low level.
When it was fixed at a low level, the user is forced to crank up the volume to hear the low-emitted tv voices. Thus, any background noise (hum) is also increased. But, but by telling the STB to produce high volume, the hum is insignificant compared to the rest of the sounds in the spectrum, making the hum appear to be non-existent.