OK, what is going on?
 

My computer fan is cycling on/off.

I've never even heard it before.

Should I open the box and vacuum out all the dust/lint/crap that surely has found its way inside?

It's 78* inside the house right now and it has been hotter but I've never heard the fan before now.

Suggestions?

Thanks.

Laptop or desktop?

Desktop.

I think I'm going to shut down and have a look inside the box.

Prob a silly question...but are you hearing the hard drive working?
The last desktop I owned...the drive was very loud.

It could well be just the fan itself is going out. The power supply itself has one fan, and likely there are others in the system. Find the noisy one and replace it. I have had the actual power supply fan dies on me. Open it up, and replace the fan. That or get a new PS fan if you don't fell like opening up the PS.

Maybe it is some other fan that is making noise.

Nope, definitely not the HD.
I have a feeling something was doing a check, unbeknownst to me, and it was working the CPU. As soon as I logged off here and went to another site, it quit cycling.
I did open it up and it's pretty clean inside so I let it be.

http://forums.pelicanparts.com/uploa...1600371521.JPG

At first I thought I'd never been inside this box. Then I remembered I put the new RAM in it when I got it.

All seems to be OK now.

My wife has the same computer since I got her one too when I found the deal on this one. Hers was making the same cycling sound the other day and she complained to me about it. It sounded normal as it stayed on steady for a while then just stopped making the noise. I wonder if some Win 10 stuff is doing a check that causes the CPU to get worked so it cycles that cooling fan shown in the picture. I don't think it runs much under 'normal' usage.

Prolly them pesky ruskies again.

Yep, some process probably got stuck. You probably could have pulled up the task manager and checked for high cpu util. I've had some dirty gear, but I've only ever had the noise increase if the fan was going bad (bearings) or the cpu was running causing higher heat and higher fan speeds. Just think of it as being like an alarm.

I'll try to remember to pull task manager if I hear it again.
Hasn't done it since this morning and the computer's been on all the time too.

Sometimes the fan is dirty, evenly dirty, and that's fine. but when a chunk of crud falls of it throws the fan outa kilter and makes it noisy

A damp cloth is good if this is the problem, yep, and a vacume.

That's normal under heavy load and higher ambient temps. If it's bothering you, you might want to look into a tower CPU cooler with heat-pipes and 120mm fan(s). I can't tell what chipset/type of CPU you're running, but there are tons of them. CoolerMaster makes some good ones. Something like this: https://www.amazon.com/dp/B005O65JXI/

Computer fans, GPU and CPU can speed up due to heat caused from load, though yours is old enough I’m not sure.