Interestingly...I did the water pump and belt kit etc on mine. It was on front ramps in the driveway for a day or so while I did bits to it. I also left it so that the sealant [for the water pump] had time to set.
Anyway, after a couple of days I finally finished and started it up and it was very noisy, turned off, left and tried again but still noisy. So I turned it off, jacked it up and took the ramps out [can't drive off them due to the front bar anyway] then started it up again and it was fine.
Oil starvation, bearing load, dry water pump, whatever, no idea, don't know. That was 10,000km ago, car is fine.