Why does my Audi A6 make a rattling sound when I accelerate?

Whenever I start accelerating, there's a noticeable rattling sound coming from somewhere under the hood. It happens more when the engine is cold and seems to disappear when the engine warms up. As far as I can tell, the car is running fine otherwise. What could be causing this noise?

The most likely culprit for this kind of noise is a loose heat shield. The heat shield is a piece of metal that is designed to protect the exhaust system from the heat of the engine. Over time, it can become loose or corroded, causing it to rattle against other parts of the car.