Why does my Audi 80 engine make a rattling noise at idle?

I noticed that my Audi 80 engine makes a rattling noise only at idle, but it goes away when I rev the engine or when the car is in motion. What could be causing this issue and is it something I should be worried about?

The most likely culprit of this rattling noise is a worn out or loose heat shield. This can happen over time due to normal wear and tear of the engine. It is important to get this fixed as soon as possible, as the noise can eventually lead to more serious issues.