In the picture ignore the diode. The armature plate which has a spring attached to it (on the right hand side) is what makes the noise. The spring tension from the attached spring is too much or the tension from the switch blades which are poking thru the plastic piece attached to the plate is too much. Try a different spring on the armature plate or adjust the leaf springs to reduce tension. This takes a little getting used to but once you get the idea you will think it easy.
