I had a knocking on my last engine, youd have sworn it was the cam, turned out to be the bottom end, confirmed this by takin a sparkplug out of each cylinder one at a time and firing it up, when I got to the dodgy cylinder the knocking was quieter due to less pressure on the bearing.... not the most accurate diagnosis but worked for me. have to agree with the other post, sounds like there are multiple knocks... or is someone at the door!