Why is my BMW 3 Series making a rattling noise when I start the engine?

I recently bought a BMW 3 Series and have noticed that every time I start the engine, there is a rattling noise coming from the front of the car. It lasts for a few seconds and then goes away. Is this something I should be concerned about?

It is not uncommon for BMW 3 Series cars to make a rattling noise on start-up, especially if it is an older model. This is usually due to the VANOS system, which controls the valve timing, experiencing wear and tear over time.