system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does the car engine sound louder and high pitched in reverse?
gpt
It's not the engine that makes that noise in reverse, it's the gear box

Reverse gears in cars are often straight-cut gears which make that characteristic whining noise.

Forward gears are usually helical meaning that the gear teeth are cut at an angle. This makes them stronger and quieter.

Straight cut gears are a lot easier to make than helical gears and since Reverse is rarely used by comparison of the forward gears then can get away with using cheaper gears.