system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do cars have those random tap/tick noises under the hood after you turn it off?

It sorta sounds like tiny pieces of sand hitting the inside of the hood or something. Since I was a kid I never understood, and I passed a car today that was making the noise after the guy had gotten out. I'm so curious!
gpt
Well, son, when things get hot they usually get bigger too. When the car is running, it gets pretty hot. So when the car stops, it gets to cooling down. As it cools down, it's also shrinking back down to size some too. Those sounds you hear are the metal cooling down. If you listen really hard, you can hear those sounds other places too. Like the flat panel TV in the living room. Some of those make sounds you can hear when you turn those off too.