Why is my Audi A4 making a loud knocking noise when I accelerate?

I have noticed a sudden loud knocking noise coming from the front of my Audi A4 whenever I accelerate, especially on the highway. It seems to go away when I release the gas pedal. What could be the cause of this and how can I fix it?

This could be due to a worn out engine mount, which can cause excessive engine movement and knocking noises. It's best to have a mechanic take a look at the engine mounts and replace them if necessary.