Tristan18au, what you are hearing when you rotate the engine to the top of the compression stroke with the tappet cover removed is compression blowing by the rings into the crankcase. This is perfectly normal, even on a fresh engine, and happens even with the cover on but is only evident to you when the cover is removed because removing the cover allows you to hear what is going on inside the crankcase/timing/cam/rocker areas better.
In short, do not worry about it. Just do your normal routine maintenance, monitor your oil consumption, ride as normal and the world will be a better place.