I have a Dell Latitude 7490 laptop, and I was faced with a similar issue. Usually, the fan runs smoothly, but sometimes it starts working as a pump, increasing and decreasing the revolutions about once per second.

After restarting, a fan failure message is also displayed, prompting you to run diagnostics by pressing f5. Diagnostics do not find problems, and after that the message about "fan failure" sometimes disappears on subsequent launches.

I have the latest BIOS version (1.6). Resetting BIOS settings to factory settings also does not help. Sometimes a reboot solves the problem.

It seems to me that this “pumping” effect occurs when the fan exceeds a certain frequency, or when it sharply raises the frequency. After the fan slows down, the next starts can be smooth even without rebooting.

I did some stress tests. The sound of the fan processor increases smoothly for 1 minute, after which it operates at a constant speed without any jumps in rotational speeds. The temperature of the processor is kept at values ​​of about 75-80 C.

Thanks for the reply - our issues sound the same.  The fan does have a pumping sound, like a whoosh whoosh whoosh noise as it speeds up and slows down over and over and over (Can go on for 5 or 10 minutes).  Agreed Diagnostics find nothing wrong.  I have the suspicion that this issue is linked to updating the BIOS.

The issue on the same laptop just started to present itself once again since I made the last post.

Has Dell got a fix for this issue or should I just RMA this laptop? Its under warranty and quite frankly, I don't feel like doing Dell's job for them in trying to diagnose under what conditions this keeps happening.

I have a Latitude 7390 laptop which works wonderfully, so I'll likely move the user on to this and RMA the 7380 if I don't get any useful information to fix this issue.

PS. On this 7390 I kept default BIOS and did not update... no swoosh swoosh fan noise!

This guy might be on to something:

https://www.youtube.com/watch?v=ughnEQL_Fks

When he mentions that the BIOS tells the motherboard not to send energy/power to the fan.

If you read my issue - the laptop suffers from two different issues. 

One - upon boot the BIOS/Laptop doesn't detect the fan and says the fan is not functioning and it halts the boot process.  Diagnostics do not find anything wrong.

Two - The fan sometimes spins abnormally and makes a swoosh swoosh swoosh noise as it speeds up and slows down.  This typically occurs either when the laptop comes out of sleep mode or from a cold boot.  It's not always - but sometimes.  And as I say, a BIOS reset seems to clear this problem for days/weeks until it re-occurs.

I have Dell Precision 3520 and I am facing similar issue. I was trying to run diagnostics bug it never found anything. I was usually able to get rid of the noise by running some performance intensive tasks and after a fan started spinning at the highest speed then the issue disappeared but reoccurred after some weeks/months. Recently I found following thread: http://forum.notebookreview.com/threads/dellfancmd-%E2%80%93-tool-to-enable-manual-custom-control-of-the-laptop-fans.827106/ and it was really helpful because I was able to execute following command:

DellFanCmd.exe ec-disable

It also set the fan to run at "100%" and after a while I executed second command:

DellFanCmd.exe ec-enable

And the issue was gone. Today I wasn't able to get rid of the noise for about 2 hours and half. I executed diagnostics again and it finally found the error:

Error code: 2000-0511
Validation: 121855
Fan - The (Processor Fan) fan failed to respond correctly

Thanks man for this tool. It is very useful but only allow 0%, 50% and 100% fan speed.

I'm really amazed that Dell has had this problem for so long and has done nothing fundamental about it.  I bought a Vostro 7590 in early May 2020, and it started failing immediately.  After the usual phone consult, time waste, Dell sent someone to replace the motherboard, but afterward, he said the fan had failed, and that he would order a new one and be out in a few days. 

Silence.

I called Dell, and nothing had been done.  A repairman was sent with a fan, which of course, didn't work.  After Dell attempted to convince me it was OK to be without a PC for 5 days while they fixed absolutely everything and return it "like new" (that's called a "refurb"), I told them I wanted a really new replacement for their lemon.

After waiting 2 weeks for the replacement, they cancelled the order--turns out they didn't have the working parts to build the Vostro 7590 that works.  I'm now waiting, and waiting, and waiting for them to build a new laptop, new model to replace the lemon. 

I've had Dell units for 30 years, but never, ever imagined I would have to deal with such rotten corporate service.  And despite the fact the unit is a lemon, it's holding up extremely well with the fan used to cool the monitor.  But I'm careful with it. 

I have the same issue now. How can I measure the temperature? I can't touch the laptop top during this time ... too much heat from the fan side.

Thanks for your post.. I've been living with this error for 1 year.

( 1)My PC is silent, does not heat up

So why the error alert?

I will try some of these suggestions. If I fail..I am OK using the PC as it is..just the nuisance error msg!

DELL AIO PC BOOTING ERROR
OptiPlex 9030 AIO PC
Alert ! Power supply fan failure .
To continue press F1 key
To change setup option press F2 key To run onboard diagnostics press F5 key