"Tac Tac" sound when printing with ABS
@Ecnerwal is right: that noise you hear is the extruder not being able to push the filament, and the stepper can't push any harder. When the extruder tries to push harder than it can, it gives up, and the "spring" tension it created in the filament forces it to go backwards a tiny bit. Then it tries again.

Possible causes/fixes:


Temperature too low -- this makes the filament not liquid enough to push through the nozzle easily. For ABS, you should be in the 230-240 range.
Clogged nozzle -- take the nozzle off (while hot) and try heating it with a torch to burn out anything that might be in there.
Bad filament -- If the filament has contamination in it, or is too large to fit through the hot end in places (I.E. it gets up to 1.9mm instead of 1.75mm)
Stepper current too low -- I'm not sure if you can adjust the current that is sent to your stepper motors, but if it is too low, the stepper can not provide enough torque to push the filament through. I don't see the stepper drivers on the site, so I don't know if you can adjust them or not.