A bicycle is quiet while you pedal and ticks while you coast, which is the opposite of what you might guess. Inside the rear hub, small spring-loaded catches called pawls sit against a ring of teeth. When you push the pedals they catch and hold, and the wheel turns with your legs without a sound. When you stop, the wheel runs on ahead of the gears, and the pawls ride up over each tooth and snap down off it: that’s the ticking. Some riders pay extra for hubs that click louder, and some engineers have spent years making hubs that don’t click at all. But on an ordinary bike the noise only starts when you stop working. It’s the sound of the machine letting go of you.