1994 Toyota Tercel OIL LIGHT ON WHEN OPERATE IN AT NORMAL T

Engine Mechanical problem
1994 Toyota Tercel 4 cyl Front Wheel Drive Automatic 120.35 miles

I REBUILD THE ENGINE,I REPLASED THE OIL PUMP
AND OIL PERSSURE SENDER UNIT BUT WHEN ENGINE HAS NORMAL TEMPERATURE THE OIL LIGHT
COME ON ,I EAR NOISE FROM INSIDE OF VALVE COVER,TELL WHAT CAN BE,THANKYOU.