system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is that tinkling, metallic sound cars make when you turn the engine off?

Is the car settling like a house?
gpt
I know exactly what sound you mean!

The sound is coming from the catalytic converter. When the engine is running, the catalytic converter is *really* hot (that is the point of it, it helps breaking down unburnt fuel and other "bad" waste products from the engine). The catalytic converter consists of a whole bunch of extremely thin tubes, and when the tubes start to cool down, they also start to contract. The tinkling sound is coming from when the tubes contract enough to overcome friction and so they move just a little bit and emit a "twink". Many tubes combined, and you get the twinkling sound.