4stroker

Just purchased an 05 XTZ 125 for cheap and was wondering about the noise it's making in the top end. Only while driving it, it starts to make some rattling type sound in the higher rev range. Any ideas? Starts fine and runs fun but just noisy top end it seems. Also wondering if anyone knows what bikes us the same 4 stroke engine? It's a pain in the ass to find parts for this thing, at least on a english website. Wouldn't mind possibly bumping the power up either with new piston or something. Ive read that the XTZ 125 possibly shares the same engine as the TTR's, don't suppose anyone could confirm this?