In the game, the vehicles have this engine sound feature where the RPM does some kind of throttle blip/wobble whenever you shift gears. This is only an auditory effect, it's basically a fake RPM blip and not a real one as car RPM and car performance is unaffected. It makes cars sound like there's some kind of excessive clutch slipping whenever you shift and it sounds off to me.

This mod disables it globally, which makes shifts sound a bit better at least to me. It was one of the bigger things that bothered me about this game. I could see why some may prefer to have it, though.

Comparison Video