Noisy engine tapping? Can I fix it? Citroen C1, Toyota or Peugeot Engine

I have a go at fixing noisy engine tapping. Could it be sticky valves or Hydraulic Lifters? How do you fix noisy tappets? How do you fix a noisy engine. Citroen C1, Toyota Aygo and Peugeot 107 engine noise. God knows what to do next...