What is the root cause of the engine knocking sound in my Audi 80?

I have noticed a knocking sound coming from my engine while idling and at low speeds. It seems to be getting worse over time. What could be causing this and how can I fix it?

The most common cause of engine knocking in Audi 80s is low octane fuel. Make sure you are using the recommended octane level for your vehicle.

Another possible cause could be worn out spark plugs. It is recommended to check and replace them if necessary.