A friend dropped a Yamaha DT250a off to me. It runs really, really well other than a bit of a rattle. This video/audio makes it sound a little worse than it really is. My son was putting some miles on it in the dirt at our house (we have a few acres) and have trailer-ed it to some woods. Not sure if the oil injector is working as it should so we put pre mixed oil / gas in it. Couldn't ask for a better running bike. Just has this rattle. Any ideas??? Thanks!