As far as I can tell neither Dave or I were saying the noise came from a loose fitting rod. We were arguing that the rod can be under tension.

As for the detonation, XJet simply said the noise mysteriously went away, he made no mention of richening the mixture. Personally I doubt it was detonation in the first place because detonation will normally show itself at full load at the point of maximum torque. The engine in question was a .76 driving an 11x7 prop so should have been running well above max torque revs. Even at peak torque you won't get it unless you're pushing the engine to its limits with the highest nitro, a totally incorrect plug or badly cowled and overheating.