It sounds a lot worse than it is, your RC car isn't going to blow up, but there is a problem.

Detonation happens when your mixture is too lean, This is when the air and fuel mixture ignites prematurely. It happens in different places in the chamber all at once, you can normally hear it when it happens and your can will loose some power, but it's not a major problem unless you don't pit. If you continue to drive you will damage your engine.

This causes pitting on the piston, head and glow plug. If you see pitting it means you are running too lean, you need to richen the mixture slightly