Cv, try disconnecting the sub and the internet from the avr.
rrlev, great instinct. I had already tried disconnecting the ethernet cable from the AVR with no change, but I hadn't tried the subwoofers. Pulling out Sub 1, the hum disappeared almost entirely. Plugging it back in, it was back in full force. Sub 2 pulled, no change. I had re-checked the ground screw on Sub 2 yesterday, but I hadn't yet re-checked the one on Sub 1, since it's more of a pain to pull away from the wall to have access to the back. After I un-screwed it a little more and plugged it back in, I'm treated to the same silence. Whew.
Mojo, I'm so sorry I put you through the mental exercise. I appreciate you putting so much thought into the troubleshooting. But I still have no idea why the hum got worse after introducing the line filter. It wasn't a subtle difference. The only thing I can think is that maybe the power cord of the power strip I was plugging the line filter into bumped the ground screw on the back of the EP800 just enough to make that difference. That's the most plausible thing I can think of.
Replacing an EP800 at around the same time as the upgrade to Actives made me assume the new hum was an Actives thing, especially after reading someone else was having a similar experience with the Actives.
I'd better go enjoy my system before I mess it up again.
