Its possbile that the lifter galley could be plugged up with something,. But if it is, you have to question how the rest of the motor is and how it was treated. I dont know if you, but look down the valve cover or somethng and see if you can see inside. Look to see what color everything is and if theres any build up.

its either that, or a lifter is going bad. Or its a bottom end noise