In reply to johnpuddephatt: Cheers John, just did the PS3 format. A bit of an improvement i.e. got blu-ray to run for 10 mins before noise kicked in and the machine will idle with no noise for hours. It didn't do this previously. I think this has nothing to do with format, it's just the newly applied thermal paste settling down (I applied this 2 days ago).
My understanding was that the fan test can damage the machine?
I have the machine raised off the floor and I was meticulous when I took it apart: used canned air, brushed the fan blades with a toothbrush, pulled string back and forth through all the cooling fins / radiator structure coming from the heatsink.
I think, as many do, it's a manufacturing defect. I bought the machine used so have no comeback against Sony.