Strange knocking?

The car is perfectly kept and serviced with ams oil 10w-30. I am from (Jamaica) the car has a minor exhaust system set up it had received a minor tuning from Elite performance. It runs nice and all however I burst a top hose one night coming in and bought a hose and install top up with coolant I saw 3 small oil spot in my reservoir bottle but none in engine oil(checked dip stick) the radiator cap has a small amount of creamy color. I bought all seals included head gaskets engine oil filter transmission oil etc. When they installed the engine, it idles and cold started normal however when revved at 3,500 RPMs it knocks, the remove and 1 off the four conrod bearing was so slightly dragged I doubted it was even a mark anyways I bought new conrods and piston rings and they re assembled and same noise. All internal components are fine no shavings no wears nothing at all. The flex plate checked oil pump checked no signs of oil starvation on the inside. No one can fine the problem they just say buy new engine.