Several things need checking. First, what weight
oil are you using? Too light may result in lower
oil pressure. Also, certain
oil filters create too much back pressure resulting in low oil pressure in the engine. Also, are you running oil cooler line or a remote filter?
A knocking sound may be caused by an underpressurized or sticking hydraulic lifter OR perhaps a connecting rod wrist pin fitted too sloppily in its piston. A sloppy wrist pin will knock when cold and disappear when the motor is hot. At any rate it sounds like you have tome serious diagnostics to perform before the entire motor waves bye bye. Good Luck.