Frustrated Runner

Can anyone help please. I have a 2000 Y reg Galaxy. Its been running fine. Then without anything happening it suddenly starts bleeping and the oil light flashing. Oil levels checked and they are fine. We have changed the oil and filter, replaced both oil pressure switches and the oil temperature switch, Still does it once you get too 2000 rpm. Stay below 50mph in 5th and your fine .... Have had the pressure inside the engine checked and again, nothing wrong, engine fine, but go over 2000 rpm and off it goes, bleeping and oil light flashing. Any idea what the problem might be... I am open to any advice, thanks Rich