Inspiron Fan does not turn off when external display is plugged in

HI,

I just bought an Inspiron 7520. It is great, but when I plug in an external display (VGA or HDMI or both) the fan starts and does not stop. Even if the laptop is cold.

There is no setting in BIOS (version A10), and HW monitor software are displaying 2 GPU fans only, with constant 1200 rpm.

Do you know any solution on this? I really would like to use the laptop with external monitors....

Thanks!