Some years ago at an garage closing down auction I bought a case with all the professional kit to do just that, it wasn't wireless back then, but had four microphones and lengths of wire connected to a control box and speakers so it could be fixed to various parts of the vehicle and then you could isolate where the noise was coming from.What an interesting way to approach this. I'd never have thought to do this. Do take some pictures so we can all understand better how you're doing it.
Sadly as I never used it I sold it on.