Niether of us thought that a flywheel could be a problem, but I remeber reading on here if it rattles then it is bad. I could hear it rattle, but moneybags couldn't. It is really a faint rattle. So we swaped it out to my running bike and it didn't run, so we put mine on his and his ran. I thought that a flywheel was just a chuck of metal with magnets glued on it, but I guess there is more too them. Swap it out and see if that is it, it took us about 30min to do that.