Hey I used to own a Tamiya radio controlled electric powered car. I think I know the sound, it's all gear noise.

Does it sound like the noise you get when you drive in reverse, only much louder?

If so, then welcome to the wonderful aural world of the straight cut gear... sometimes referred to as dog gears or dogboxes. These are the most bulletproof types of gearsets because they are much beefier than regular gearsets. They are also resistant to sideways shearing forces that plagues regular helical cut gears and are apparently easier to swap out in service when seconds tick. Their major disad is the noise. All gears sound like reverse in a regular manual car except louder still, especially so with WRC cars because of the lack of sounddeadening and acid dipped frames (no sound muffling undercoating).

 

Don't forget all these WRC cars run anti-lag turbo systems, which are pretty load, and when braking etc, these will be still firing fuel into the manifold to keep the turbo spinning, pops and bangs everywhere...