thanks, guys. I wondered why my isolation transformers seemed to be humming more loudly since I moved from a dedicated-line house to an apartment with inferior power. There's no help for it though; they're needed more than ever where the power is bad. I've been trying to think of ways to deaden the sound. I understand that Shunyata's have a box-within-a-box design, with soundproofing between them, to address this, but a diy attempt at this would seem to create heat issues.