I have a dell optiplex 9020 that has an unusual problem. The unit works fine, powering on and running normally. No issue with stability and performs as expected. However, as soon as power is applied to the unit (i.e. power cable plugged in) the fans spool up to full power. The fans remain on 100% until the power button is pressed, following which they spin down and act normally. I have updated all drivers and bios, tried disabling C-states and changing any remoterly appropriate bios options. Anyone got any ideas?