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

I was editing a scene last night — dawn light on wet pavement, a bus pulling away with its doors hissing shut — and I kept pausing on this one sound: the soft click of a woman’s heels on a crosswalk, then nothing. Not traffic, not wind. Just that single step, like she’d stepped into silence. I started wondering what else we miss when we’re just passing through. What tiny things do you carry from your days that no one else hears?