Nissan Repair: oil light stays on, oil pressure sending unit, oil starvation

Question
I have a 2k niss.Sentra 1.8L and the oil light stays on and seems as though while its on , no oil is getting to the top end , and you could hear the valves tapping . All knowledge says that it should be the oil pump. Without it being the oil pump though , WHAT else would cause that ? Is it possible to have a clogged oil pump ? Also , if the sending unit was bad that wouldn't cause the oil pump to stop working right ?

Answer
Victor,

A clogged oil gallery that feeds the head could cause the oil light and ticking.  I would suggest first the oil pressure sending unit be replaced to see if the light will go off.  The ticking up top could be resolved if it is getting oil and the rockers just needed adjustment.  If the sending unit is replaced and the oil light is still on would lead me to a oil pump replacement to see if that resolves the suspected oil starvation on the top end.