hey sepp, that's pretty common and it's the hinges themselves, the pivot pins get a bit worn and the springs move them around in the holes ... you might not be able to spot the movement messing with the hinges by hand, but those springs exert a lot of force, in different directions depending on position of the hood - try the hood without the springs and you'll find it works fine and sits flat when closed, add the springs and it goes snakey .... just need new hinges to go with those new springs
Bill