Is it normal for a fan to make a noise when it starts and when it stops?

[mpw101]

Product number 6YQ50AA#ABA

Microprocessor Intel(R) Core(TM) i5-9400 CPU @ 2.90GHz

System board 8653 A (SMVB) System BIOS F.20-5/29/2020

Windows 10 Home v1909  64bit

Windows Firewall and Windows Defender

When I turn my desktop on something starts with a one second whirr sound.  I guess a fan is starting.  Probably normal. 

When I shut down my desktop something goes clunk.  I guess the fan is stopping.  Probably normal. 

When I am surfing the internet, from time to time I hear the very brief whirr sound.  I think the computer just gets busy and the fan starts up.  Might happen when I open Office Outlook sometimes.  Probably normal for the fan to come on when the computer gets busy.  I think it is designed to cool things down. 

What I am less sure of is while just reading something for a while, not changing web pages, no video playing, for no apparent reason, when the desktop is quiet, it just goes clunk.  Is that the fan stopping? 

It is entirely possible the fan has been running; it is so quiet I just don’t hear it.  I just hear the clunk when it stops.

The internet is full of horrible things when you search for computer noise but they all seem to be about continuing noise or clicks.  That is not what I am hearing. 

I am asking if it is normal for a fan to make a one second whirr when it starts and a single clunk when it stops.  And if this is normal to happen during a time when the computer is in use, not just when I turn it on or shut it down.

[WAWood · Accepted solution]

@mpw101 

Different model fans make different sounds, and while none of mine make the "clunk" sound when spinning down, that does not mean that yours will not make it.

It is normal for the system fan to spin up when processor demands increase, so you will hear that whirring sound.

Other than replacing the fan, I don't know what to suggest because we don't have any diagnostics for testing fans.

[mpw101]

Thanks. I just needed some reassurance. 

I was pretty sure the "spin up" was normal and that is exactly what it sounds like by the way. 

I was just not sure about the clunk noise, which sounds like something that has been spinning fast coming to an abrupt halt.  It doesn’t spin down; it sounds like it just stops instantly.

I don’t actually hear the fan at all after it spins up so I think it is OK. Actually, the desktop tower is very quiet.  I guess that is why the occasional clunk when the fan shuts down is so noticeable.

Thanks again.