Why is my Audi A4 making a rattling noise when I start the engine?

I recently purchased a used Audi A4 and I noticed that when I start the engine, it makes a loud rattling noise. It only lasts for a few seconds and then goes away. What could be causing this and should I be concerned?

The rattling noise you're hearing could be due to a loose heat shield or exhaust bracket. These can easily be tightened or repositioned to eliminate the noise. However, if the issue persists, it could be a sign of a more serious problem such as a failing catalytic converter. It's best to have a mechanic inspect the car to determine the cause.