What sort of a sound does detonation make in a 2-stroke glow engine?

I have a 50 sized 2-stroke that makes a clattering sound at certain rpm. I've taken it apart and it seems to be in great shape inside. I'm wondering if the clattering could be detonation? I'm running 15% nitro fuel and an Enya #3 plug. The clattering seems to be sensitive to mixture - if I lean it out the sound goes away or moves to another rpm.

I'm running it on a test stand and am sure the noise is not a mechanical resonance exterior to the engine.

Thanks for the help. This forum is a wonderful resource.