It's a complex thing to diagnose and fix judging by how much reading i've done over the net the last couple of days - not sure i'm quite yet ready to write these off and blame the manufacturing (but this product does seem to highlight weaknesses as evidence by how much internet chatter there is with the A5 and humm/buzz).
I'm not a tinkerer by nature, but forking out so much (relative) money for these, the Audio-GD Fun and Interface, I have to try before sending them back.
It's like the old days of TV holding the TV aerial and walking around the room to get the best signal :-) If I turn the active monitor 45 degrees off axis and hold the y-split mini to RCA, it reduces the buzz to only 30-40% of the full level, or slightly better if I get the wife to stand in front of the drivers when the active speaker is 45 degrees off axis - not an ideal solution there....
I've plugged a Tacima mains conditioner in - zero difference.
Tried a difference AC point (basement) - 10% interference, not too bad - can't live in the basement though :-) Might drag them off to work, try them there (brand new building running a data centre).
Have the Belkin isolator on the way, a C14 to C7 adaptor - not made my mind up on going crazy on a new AC cable, but have a decent one that shipped with my PC and has the ferrite clamp built in, so will try that.
Agree though, it's annoying - hurts my ears :-)
Oh yeah, I'd say the buzz is 110/112hz.