When during printing you hear a clicking/ticking noise coming from the print-head. It is most likely the sound of the stepper motor stagnating and skipping a motor-step. This is not harmfull to the printer or motor. The most common causes for this.

• Extruding too fast at to low temperature.
• Printing at a too high infill, where nozzle exit is blocked by printed object.
• A clogged hot-end. Please read this article for troubleshooting this issue.