Adding a 3d sound source for an object in your project is very easy.
Custom made sound effects (.wav, .ogg files) can be used with the SoundSource object as described in the
documentation.
In this movie I apply a car engine sound effect to the default buggy car.
The first thing I do is placing the 3d cursor where I want the sound source, by right-clicking the car engine.
My SoundSource object settings should simulate gear-shifting audio pretty well for the default car,
but you may have to do some tweaking if you change car's top speed, acceleration, etc.
Please allow some time for the movie above to load. If you can't see the video after a reasonable delay, please
click here. Note that this clip has no audio.