TV and Tube gear.

Thank you all very much. I will give it all a try.

If isolating the CATV's ground doesn't cure this (just disconnect the CATV to determine if that's the actual cause) then try isolating the TV's audio ground from your audio system's ground. If that's the cause of hum then you'll need a pair of inexpensive audio balancing transformers, which can be found at car audio shops & supplies. I ususlly find them as two transformers built into a single package with four short cables dangling out (two in's & two out's) color coded for left & right channel.

You have a ground loop caused by components that are grounded at different potentials. If you have cable TV, that's the most likely candidate.

Connect a pair of 75->300 ohm Baluns back to back, and put that in the cable line.