Why does my Audi 80's engine make a knocking sound when accelerating?

I've noticed that my Audi 80 makes a knocking sound when I accelerate, but the sound disappears once the car has reached a constant speed. What could be causing this issue and how can it be fixed?

This knocking sound could be a sign of engine detonation, which can be caused by a variety of factors such as low octane fuel or dirty spark plugs. It's important to get this checked out by a mechanic as soon as possible to prevent any potential damage to your engine.

Another possible cause of this knocking sound could be worn out engine bearings. This is a more serious issue and it's best to have a professional inspect your engine to determine the exact cause and solution.