Vehicle Noise Synthesizer
From the project git:
“VNS is an open-source free audio addon primarily designed for Unity to simulate vehicle sounds based on engine rpm similar to a granulator without dependencies such as FMOD”.
Vehicle Noise Synthesizer is a 3rd party add-on provided by imDanoush (Dan).
More info: https://github.com/ATG-Simulator/VehicleNoiseSynthesizer