The act of hitting something in hopes it will make it work.
Sometimes, it is the only way things will work.
Mounting your fan like that wont hurt it. If it was that screen making the noise, you would hear loud whistling, so unless you hear that, it is not the mesh. If you cover it with a peice of paper, it is sucking as much air around it as it possibly can whilst covering the fan with the paper, dramatically reducing air flow. The onyl thing i can think of is that it is rattling, or the fan is on it's way out.