I have replaced my 4.7 liter engine in my 2002 Jeep grand Cherokee with one from an engine builder. We drove it 1300 miles changed the oil @ 500 miles with about 1/2 quart of loss for break in. Conventional oil 5W30. Drove 700 miles after oil change. Oil level is full. Left side of engine started making lifter noises suddenly, like no oil pressure. Right / Passenger side is quiet. Mechanical oil pressure test. Cold @ idle 73 psi; Cold @ 2000 rpm 83 psi; Warm @ idle 40 psi; Warm @ 2000 rpm 74 psi. Left bank of lifters still making noise during the test. Now there is evidence of oil leaking from the left side of engine also. Is there an oil port plug on that side of the engine that could be leaking and letting the oil pressure out? What could be causing the issue?

 

If it was leaking enough to let the lifters rattle, it would likely pump the engine dry pretty quick, still, oil leaks at gallery plugs are bad news.

Any warranty from the builder? Think I would have a chat with him.