This is something I have been curious about since childhood and I still don't have the answer. I have theories about the answer, but I figured this is the best place to find somebody who knows the facts for a certainty.

I am wondering exactly what is responsible for the change in sound when a car is in reverse gear rather than moving forward. The sound, almost like a winding noise, is something easy to pick up on, you can tell the direction of travel with your eyes closed. One of the most famous examples, in my mind at least, takes place in 1964's Goldfinger. James Bond's famous DB5 had a great engine note. There were several examples note change, one where he backs up at a service station and others during the climactic chase that led to the car's destruction.

The sound change isn't present in all vehicles. I've noted it seems more common with standard drive transmissions rather than automatic. I understand most of the engine sounds in movies are highly edited and often dubbed, so this is based on actual observations as well as what's on the big screen.

I thought it may be related to simplicity of mechanical transmissions, but even my automatic drive 2013 Honda Accord makes the whine too. It's not a CVT, but I assume a transmission that modern would be electronic and computer controlled. The blows some holes in my mechanical theory, so I'm very curious to learn the real reason.

Any explanation you can offer would be greatly appreciated!

Max Power

For reverse drive, I think that there is an extra gear + a different kind of gear than for normal drive, making then a different sound.

A note about speed rather than sound, the DAF 600 could go as fast in reverse than in normal drive, because of a non limited CVT transmission (Variomatic)
https://en.wikipedia.org/wiki/DAF_600

In a manual gearbox the forward gears have helical teeth to reduce sound, the reverse gear have straight teeth.