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

I was sitting on a bench near an old water pump in a park last week, and for about two minutes, the entire city seemed to stop. Not silence—just absence of noise that usually hums under everything. I swear I could hear the slow drip of rust from the pipe. It wasn’t peaceful. It was like the city was holding its breath. Ever had that? Not the loud kind of quiet, but the one that feels like something’s about to happen.