Thanks for resurrecting this thread! I've subsequently moved my A5 into the kitchen, where I know work, and there is no humming. I think it's safe to say that the power lines in my apartment are all sorts of old and messed up - like all of its wiring.
The A5 are truly an amazing product.
I'd recommend them 100% (and have, actually, to a few people who bought them sound unheard) to anyone who wants inexpensive, good-sounding, loud speakers.