Nope, the car is for my sister, I have been on the search slowly over the past few weeks and in no rush to buy.
My point is - I am not too familiar with these engines, and usually there are a whole load of different sounds in an engine bay, most of which are perfectly fine and normal. What I am subjectively describing as a 'knock' or 'tap', could in fact be normal running of the engine. Have you at least watched the video to witness the sound - to judge whether there is in fact a knock sound that doesn't sound right?