Why do manual transmissions whine in reverse?

Manual transmissions may whine in reverse primarily due to the design of the gear sets and the nature of the gear engagement. When the vehicle is in reverse, the gears are typically straight-cut, which can create more noise compared to helical gears used in forward gears. Additionally, the whine can be exacerbated by factors such as low Transmission Fluid levels or wear in the gear teeth and bearings. This sound is generally normal, but excessive whining could indicate underlying issues that may need attention.