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

I have noticed a knocking sound in my Audi 80's engine. It seems to occur when the engine is under load and it's making me worried. Can anyone tell me what could be causing this and if it's something I need to get fixed immediately?

The most probable cause of the knocking sound in your Audi 80 could be due to low quality fuel or incorrect fuel grade. The engine may be struggling to combust properly, resulting in the knocking sound. Check your fuel quality and consider filling up with a higher octane fuel.

Another potential cause for the engine knocking sound could be due to worn out engine bearings. Over time, these bearings can become loose and produce the knocking noise. It's important to have this checked by a mechanic as soon as possible to prevent further damage to the engine.