Why does my Audi A3 make a rattling noise when I start the engine?

Every time I start my Audi A3, it makes a loud rattling noise that lasts for a few seconds. It seems to be coming from the engine area. What could be causing this and how can I fix it?

The most common cause of this issue is a loose or worn out serpentine belt. This belt drives multiple components in the engine, and when it becomes loose or worn, it can cause a rattling noise. I recommend having a mechanic inspect and replace the belt if necessary.