What’s the quietest thing you’ve ever heard in a live panel?

Just finished a safety check on a 480V substation, and for a second—just one—the whole thing went dead silent. Not even the hum. I swear I heard my own breath like it was coming from inside the cabinet. It wasn’t the voltage dropping; it was the air itself holding still. Since then I keep wondering: what’s the quietest thing you’ve ever noticed in a system that should be alive? Not noise—just absence. Like the wire remembered something.