Just off the top of your head. My little puch e50 has a problem with high rpm "rattling" "buzzing" hard to describe really. It's happening right at the combustion chamber (easy to locate noises on this little exposed engine). It could be electric, fuel, compression, vacuum leakage, etc etc. I could describe the bike to a T but it might not help. I wonder if anyone with small two stroke experience might chime in with "check your...). Fine idle. Fine midrange. Fine, in fact, in most circumstances. When going uphill, or against the wind, at high rpm the engine starts hesitating and each hesitation is accompanied by this sudden onset of buzzing or high frequency rattling from the head. I can add more info if needed if anyones interested in guessing.