Why does my Audi A4's engine make a rattling noise while idling?

I recently noticed that my Audi A4's engine makes a loud rattling noise while idling. It seems to go away when I accelerate. What could be the cause of this and how can I fix it?

The most common cause of a rattling noise from an Audi A4's engine while idling is a loose heat shield. This can easily be fixed by tightening or replacing the heat shield.

Another possible cause of the rattling noise could be a worn out timing chain tensioner. This can be a more serious issue and should be looked at by a professional mechanic.