Whilst embarking on some updates to my ML115 I decided to update the BIOS as the version currently running was approx 3 years old and I have been having a minor issue recently which I was hoping that this would resolve. So I downloaded the BIOS from the HP site and installed via USB key all without a hitch. I then came to reboot the machine and the fans which used to spin down following the POST now run at full speed even once the OS has loaded (OS being ESXi 4.1).
A bit of googling pointed me in the direction of the update for the iLo firmware. It appears that it is required even if the iLo card is not being used as it is stored on the mother board. I do not have the optional iLo card so overlooked this update initially.
iLo firmware updated and now the Fan noise is no more. 🙂