Andi, it is very hard to diagnose noises on the internet, I suggest that you take it to a Local Indy and hopefully find an inexpensive fix
Haha, I do like those type of problems. There should be a rubber grommet on the cover that the tube goes through and is quite a tight fit. Sourcing one from your local hardware store shouldn't be much of a problem.Thanks for all the replies guys, I found the knock. It was the Dipstick holder knocking against the hole in the plastic engine cover lol