Dont the cam phasers usually make a ticking sound? I've got that problem too lol, but im talking about a low knock.
I am using mobil 1 oil 5w20 and the knock does not just go away right after start up, it continues to knock until the engine warms up a bit. It usually knocks for a good minute to two minutes, it knocks until i am at the second light or so out of my neighborhood, so its not like that sound you usually get right after an oil change and start it up for the first time when there is no oil being pumped for a second or so. It only does this in the morning when it is cold out.