With latest fw and XPEnology fan work over 30-35%. XPE not have the right driver for hdd smtemp sensor. On ESXI with correct driver on it, fan work on 6-10%.
I choose ESXi for low noise and Raw mapping drives to XPE virtual machine. like a post on this forum
I have virtual XPE on 2.5'' hdd drive on bay 5 (odd)