My extruders ticked, much dismantlement later with much cleaning and reassembly and it still ticked. I then noticed that it only ticked in the Y axis direction and it turned out to be loose ends on the layshaft at the top rear of the machine. The noise was absolutely the same as slipping filament but only in the Y direction.

Long shot but easy enough to check, with the machine off, manually move the head and see if it ticks.

My machine is a Wanhao.