Sir, That seems pretty much par for the course at 272K+miles. Tolerences in both the oil pump and the mains (which is where the noise eminates) have increased. Nothing to be alarmed about. Good quality oil and a full crankcase of it is your best bet. When oil levels are lower than full, especially with a pump having been quite well seasoned in, it surely could take a little longer to pump up. The sooner, the better