Well, the noise is gone (at least for now)
As I wrote before, my crankshaft vibration damper was worn (see photos) . On the first photo I press the two metal pieces to eachother. You can try this while the damper is on the car. On a good damper this should be solid (not to be pressed). On the second photo you can see the space between the plates.
The damper has been replaced today. Also my engine mount (RHS) has been replaced and the noise is gone
. I hope the problem is really solved. I would say: check these two parts and replace them if they are worn (I found a second hand damper in good condition for € 150,- (new € 540,-) ...