PC's fan speeds up to full for just a second after every 40-50 seconds (suspected fan: cpu), help ne

[TheVortex73]

Hello everyone!

I have a secondary pc which I sometimes use, it's specifications:

GPU: [ASUS] Nvidia Geforce GTX 750 (1GB)

CPU: Intel Core i5-2400 @ 3.10GHz

Ram: 8GB (2 sticks of 4s)

OS: Windows 10 (22H2)

Model: HP Compaq 8200 Elite CMT PC

Since recently, I started getting an error "Real Time clock power loss" during startup, but I'd press F1 and it'd boot and function normally without any problems, so I didnt pay much attention to it.

However, since a few weeks ago, I upgraded my PC to Windows 11 despite it being unsupported because I wanted to give it a shot of how it would work. For a few weeks, it worked perfectly. However, now, whenever I get to the password screen, my PC's fan, which I suspect to be the CPU's fan, speeds up for 1-2 seconds then calms back down. This happens after every minute or so. (I just downgraded back to Windows 10 and still have the same issue) 

I have checked my temperatures, they're all always under 40°C. This happens even when my pc is idle. I've checked task manager, there's no difference in any raise of the CPU Usage, or any components usage. It's all working normally except the fan speeding up for a second. SpeedFan does not detect my fans for some reason, I've tried many fixes but it just doesn't.

NOTE that this DOES NOT OCCUR whenever I boot into the BIOS. In Bios, no fan makes any noise of any kind whatsoever, its all smooth.

Can this be related to the dead motherboard/CMOS Battery? 

Help is appreciated.

Thanks.

[lord_nuker]

The first error relates to an failed Bios battery, the fan speed is probably related to an windows power setting, where the cpu clock speed jumps up and down.