Weird sound on the start.

It’s a Rex RS 400, with 3t km. Now to my problem. Since yesterday I usually hear a metallic knocking on the start. Sounds like a screwdriver is in the tank and hits the left and right against the sheet metal. The sound probably comes from the front and usually occurs when I hit the handlebar and roll a piece slowly. Had it already rolling backwards. Tires front has no game, and when I pull the front brake in a jerky way or when I push the shock absorbers down I don’t hear anything. So far I only heard the beating noise when the engine is running and only the first few meters, or when I take a break in between and then go off again. I have always had the main stand down, but it’s kind of stuck. I’m a bit afraid that some camp is broken and it’s dangerous to drive. But a camp can be so loud and beating e Make noises ? So with the car, storage damage is usually constant noises. Maybe someone knows the problem or has a guess. LG Jürgen