Shop owner flushed the crankcase, changed oil and filter. Oil pressure is now 'decent'. 7.5 lbs at idle and 42 lbs. at 3000 rpm. The rattle is still there. Guys, this thing sounds almost exactly like a diesel or a terrible case of pre-ignition!! We pulled the rocker cover and it's getting plenty of oil trough the cam lube rail and the lifters appear well lubed. Still it rattles. Any ideas?