@manatee
I'm not sure if driving a speaker (8[ch937]) directly is a good idea. You may need to drive it through a transistor our use a series resistor. Other's will comment on this.
However to get the loudest possible click if you run the piezo on 2 pins - one out of phase with the other, you get twice the deflection on the "cone" and a louder sound.
I used this technique with a Geiger counter (only with inverting buffers) and it worked quite well. 