Researchers did find that dogs can distinguish a contraption with electrical current running through it from an identical contraption with no current running through. They theorize the dogs can detect the resulting ozone.
I was in a pet store with my old dog and he completely avoided a pillar in the middle of the aisle, sniffing the air in its direction but pushing himself against the shelving as we passed by. When I looked closer, the outlet in the pillar had a plug prong broken off and lodged in the outlet. Managment got a hefty shock when trying to cover it with tape once I informed them. There was no sound that I could hear but something about it triggered the reaction in my dog.