Why is my Audi A5's engine making a strange noise while idling?

I recently noticed that my Audi A5's engine is making a strange noise while idling. It sounds like a clicking or rattling noise. What could be causing this and how can I fix it?

The strange noise while idling could be due to a worn-out accessory belt. Check the condition of the belt and replace it if necessary.

Another possible cause could be a problem with the timing chain. Have a mechanic inspect it and replace it if necessary.