[Anker]

Why don't you figure out where it is coming from by taking the engine cover off and using a mechanics stethoscope or just a long screw driver on the two heads. If its coming from one of the heads its most probably a lifter (assuming that it isn't piston slap or bearing knocking - I assume you can hear the difference). If it isn't from the heads I would take the front cover off and check the belt pulleys after removing the serpentine belt.