looking to purchase a 2010 golf 1.6 d estate, 140k miles, it has a loud ticking sound from the engine when the filler cap is removed, not apparent when the cap is in place. It sounds like just one valve only making the noise.
The simple fact that you feel compelled enough to question the engine noise should be enough to decide not to purchase it. You will spend the entire time you own it wondering if something is about to come apart. Best to steer clear of it as it would not be an easy or cheap fix should it get worse. Just my opinion.