system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:What's actually making those ticking noises when your car cools down after being shut off?
gpt
A lot of it is because metal likes to expand when it gets hot and contract when it cools down. The borderline microscopic expansion and contraction make lots of little stress points while the material essentially fights itself to either push itself out or pull itself back into shape, and they go "ping" and "tick tick tick" sometimes when the pressure is suddenly released, kind of like canning jar lids you can press the tab in and out to go "clack clack clack" as it flexes.

It makes popping and pinging noises while it's warming up, too, but you don't hear those because the engine is running and you're driving. Wood burning stoves, furnaces, pretty much anything with drastic heat cycles will do this, too.