Why is my Audi A4 engine making a strange noise when idling?

I've noticed a loud rattling noise coming from my Audi A4 engine when idling. It seems to go away when I rev the engine, but returns when I am stopped at a red light. What could be causing this and how can I fix it?

It sounds like you may have an issue with your engine's timing chain. This is a common problem in Audi A4s and can cause a loud rattling noise when idling. You should bring your car to a certified mechanic to have it checked and repaired if necessary.

Another possibility could be a problem with the exhaust system. A loose or damaged exhaust pipe can produce a rattling noise when the engine is running. Have a mechanic inspect your exhaust system to determine the cause of the noise.

It's also possible that your spark plugs are worn out or need to be replaced. This can cause a ticking or clicking noise when the engine is running. Have a mechanic check your spark plugs and replace them if necessary.