I have a great Audio-GD power conditioner between my Mac Pro 3,1 and the wall. I went to turn on the big machine a few minutes ago, and I heard a rather loud buzz: it sounded somewhat like noises heard form cheeeep SMPS units. I followed the noise physically, eventually ended on the IEC plug at the wall. I shut everything down, switched to another cable, and we're all good.
What just happened here?