Inspiron 3847, fans won't stop revving

Dear Dell Community:

I am hoping that someone within the community can help me with this problem.

My PC fans won't stop "revving."  This problem began about a year or so ago, at first intermittently but now it's constant.  It begins when I turn my machine--basically, before the POST has had a chance to proceed--and it continues without relent until I force a shutdown (system shutdown won't quiet it).  Usually, when the fans run at high speed, it means that the machine might be overheating but when they (my PC has two fans) begin before the POST, then I assume that it's another problem.  Out of desperation, I reset my Windows OS to try to counteract this problem, thinking that perhaps my copy of Windows 10 may be the cause, but it didn't work.

I made a few notes about other oddities:

- Sometimes when I work through the revving for an hour (without earplugs), restart my machine or shut it down, and then restart it after a few seconds, the fans won't resume revving up.  This respite will last for about 20 or 25 minutes before the fans begin their maddening pace again.

- Another off-the-wall method I tried was to train a space heater at my PC for about two hours (on the side of the PC case where the fans are located) and then turn on my machine.  For a while that seemed to work; I would be able to get work done for four or five hours after that and have a "peaceful" shutdown.

- There is an odd, metallic "shifting" sound when I turn on my computer and I have found that when that sound occurs before the POST, the fans won't rev.  I am unable to locate the source of that sound and have no idea why it's important for it to occur before the POST to restrain the fan revving.  Unfortunately for me, that shifting sound usually occurs after the revving begins and I will have to put up with it until my work is done.

I am at my wit's end with this.  Is this a problem specific to Dell Inspiron machines?  And why is it bedeviling me seven years after I purchased it?

CartoonMan