Cooling Fan - Excessive Speed

I have an Alienware R4 with Bios A11 which I recently upgraded from x64 Windows 8.1 to x64 Windows 10 Pro.

The Windows 10 upgrade went off without difficulty, and for several weeks all has been well - no problems or issues using a variety of programs. I added a printer last month which has also been working just fine. No further updates or changes for at least a week, with normal daily use.

HOWEVER, this morning when I turned on my computer, the cooling fans IMMEDIATELY went to high speed and stayed there. (The vents in the case are NOT flared open.) I went to the Alienware Command Center and it showed both the PCI fan and the Hard Drive fans were at 100%, and a little padlock icon was in the lower right of each panel indicating that they were locked at that speed.

I've had no prior symptoms of overheating . . . and the system SEEMS to be working OK, apart from the noise of the high speed fans. I ran the basic Dell diagnostic tests and the unit passed all of them.

Any suggestions?