The clicking sounds are a result of an important compromise: Most instruments use a potentiometer for volume adjustment. Characteristically, they eventually become scratchy or crackle after years of use. We thought about a final VCA for the master volume, but this has the issue of a not ideal signal to noise ratio at lower settings and some distortion/colouration of the sound.
We eventually decided on a digital potentiometer. When static, it has near perfect characteristics and will never wear out unlike a potentiometer, neither will it add any noise or distortion to the signal like a VCA, however it has the drawback that there is a subtle but noticeable clicking when adjusted.
To overcome this, it is better to "set and forget" the master volume. Then use the ENV LEVEL fader in the VCA section to dynamically adjust the volume during any kind of recording or performance. This is a high quality VCA that has a much higher resolution of digital control.