The ‘clicking’ is not a fault and a known by-product of DC as it interacts with the contacts on the resistive-ladder volume control. However, the clicking should not be readily apparent unless the volume passes the 13-15 mark and again around the 31-33 mark, the two points where all the relays come in contact. There should be no clicking at all when the unit is on mute as the volume control is disengaged. It may help to short the input plugs on the back of the unit to help prevent DC buildup.