Why does my Audi's engine make a banging noise?

I recently bought an Audi A4 and noticed that the engine occasionally makes a banging noise. It doesn't happen all the time, but it's starting to worry me. What could be causing this and what should I do about it?

It's possible that your engine is detonating, which is when the fuel-air mixture explodes instead of burning smoothly. This can be caused by a number of factors, such as low-quality fuel, worn spark plugs, or a dirty air filter.