Had this problem before (we all have), just tighten the back axle and brake. With an allen wrench, size 5 or 6 metric (no scooter parts that I know of deal in American sizes, and I’ve dealt with that scooter before so I know) but you might need two, one to keep the bolt steady so it doesn’t rotate and not tighten. Tighten it until it’s you start to feel it get to the point where you can’t go in much farther, and if it still rattles, use a smaller (metric) allen wrench to tighten the brake.
