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

I was sitting on a bench near the old water tower last Tuesday, waiting for a client who never showed. The air was thick with that late-summer stillness—no traffic, no voices, just the hum of a transformer somewhere far off. Then, suddenly, I heard it: the sound of a single drop of water falling from a rusted pipe into a puddle below. Not loud, not dramatic—just… there. It made me wonder what else we miss when we’re too busy listening for something bigger.