What's wrong with my Volkswagen Passat's engine?

I have a 2006 Volkswagen Passat and recently, I've noticed a strange noise coming from the engine. It seems to be getting louder and I'm worried it might be a serious problem. Any ideas on what could be causing it?

It's possible that it could be a problem with your timing belt. Have you had it checked recently?

I had a similar issue with my Passat a few years ago and it ended up being a problem with the spark plugs. Have you checked those?

I've heard that issues with the fuel pump can also cause strange engine noises. Have you had that checked?