Loud clicking noises while printing are usually indications that the extruder motor is skipping steps, This could be due to:

• First layer or two – nozzle too close to bed
• Later layers – extruder temperature too low (not melting quick enough)
• Trying to go too fast (stick to around 45mm/s) to see if the extruder can keep up
• A blockage/clog/jam in the nozzle (very common) or PTFE tube getting tired.
• The idler arm could be cracked at the joint near the screw or the idler bearing could be worn out or damaged. These are rare instanced but have happened.

The gear could be chewing up the filament, which gets the dust debris in the teeth and reduces grip on the filament, worsening the problem.