OK you experienced sparkies...got any ideas on this? I had my hifi power amps upgraded around Xmas time, Toroidals upgraded from 500KV to 1000KV (2 mono block amps) When they're on, I occasionally get a buzzing from the toroidals, it might happen once or twice a day, sometimes not at all, and last from a couple to 15 minutes. I understand this is cause by DC on the mains, normally due to to asymmetry or harmonics in the L-N sine wave and thus causing magnetostriction in the toroidal core. This is now happening as the larger toroidals are more susceptible than the older smaller ones, but what puzzles me is that its only been happened in the last 2 months or so, it didn't happen from Xmas to April/May. I wonder if some kind of high power device has been introduced locally recently, does any one have a clue might might be causing this kind of DC on the mains? I live near a railway & station. Could it be a household appliance nearby?