There is a faint, but audible click in the audio when input is turned past 12 o'clock i.e. the upward vertical position. It seems to click (a quiet one) when you pass this position turning the input dial either way.
The Input/Output knobs are not pots like on ordinary gain or volume controls.
These input and output knobs controls a gain chip which switches the gain in small steps (dBs). Hence you will hear minor "plops" while turning the knobs.
The benefits are that this is far more reliable and precise than ordinary pots. Additionally the gain section automatically switches the input sensitivity when passing the 12 o'clock position, optimizing signal to noise.