Hammer sounds are trigger when you press the sustain pedal, release the sustain pedal, or release a key. These sounds are designed to be relatively quiet, so that they do not get in the way of your piano's notes. However, as in a real grand piano, they are part of the mechanics of the piano and add a wonderful degree of realism to a solo piano recording.
If you cannot hear the hammer sounds, try turning the hammer sounds control all the way up. You can find this adjustment on Pianissimo's Control Panel. Once the control is all the way up, press and release the sustain pedal. You should be able to hear the sound of the dampers moving off and on the strings. Now, dial back the amount until the hammer sounds are barely audible. This is a good approximation of the level of this effect in a real grand piano.
If you don't like the way it sounds, set the Hammer Sounds amount to zero.