system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do cars make relatively typical engine sounds when driving forwards, but sound like giant battery-powered RC cars in reverse?
gpt
In a manual transmission the reverse gear is a different style of gear that have strait teeth called a spur gear compared to the other gears (1st-5th for example) that have angled gears.  The noise you hear is the reverse gear is the teeth of the gear colliding which only occurs on the spur gear where the regular angled gears slide into place.