Same issue here. Unacceptable situation. [NAME]-Cares  please check it out and don't post us a screenshot of the faq saying that it's normal. IT'S NOT. I have a Latitude 7480 connected via the Thunderbolt and 2 screens. Even when the laptop is off the fan goes on and off. I have the latest firmware installed without any difference. Update= it seems that the problem has been temporarily solved by lifting the docking station so that it gets more air. If the problem re-appears I will contact you back.
My dock is loud 90% of the time.  This is the third replacement dock I have received from Dell.  Each one does the same thing.  It's either super quiet or super loud.  It's always less than 70* in my office and it's clear of obstruction.  When my laptop is in Sleep mode, the fan goes on and off all night and I can hear it a room away.  I have upgraded to the newest firmware and it seems to have made no difference.  I need resolution on this - it's unbearable during calls. Update = After completing troubleshooting, a DELL-Cares agent setup a part exchange. Resolved-The new dock is much quieter.
WD19 Dock Fan Very Loud