Why does my Audi A2's engine make a rattling noise when idling?

Recently, my Audi A2's engine started making a noticeable rattling noise when idling. It goes away when I accelerate, but comes back when I am stopped or in park. What could be causing this and how can I fix it?

It is possible that your engine's timing chain is loose or damaged. This can cause a rattling noise when idling. It is important to get this fixed as soon as possible, as a damaged timing chain can lead to severe engine damage.

Another potential cause of the rattling noise could be a faulty alternator pulley or belt. This can cause the engine to vibrate and produce a rattling sound. Have a mechanic inspect and replace these parts if necessary.