So I spent a few hours trying to trace it down, spending most of that time crying because now is not the time for a new pre-amp or amplifier — we’d just have to sit in silence (well near a hum). Luckily, it was the idiots at the cable company! I unplug the cable from the wall and the silence is golden! I can hear the fans form the computer in the other room (which is an entirely different problem)!

After several phone calls,  the cable company assured me that nothing had changed in the cable plant in my neighborhood. There were, of course, unable to explain the presence of one of their truck in the neighborhood as I was leaving on my trip — but clearly they think I am an idiot for trying to hold them to a reasonable level of service… I guess they’re named COX for a reason!

Dayton VIT-1 Isolation Transformer
Price: —

1 used & new available from USD 9.49

So I ordered this isolation transformer from Amazon, installed it, and my problems seem to be gone! I’ve still got excellent picture quality and signal strength, but the nasty ground loop no longer makes it painful to sit in that room.