CPU Fan continuously running at high speed & loud. Also surges (in speed & sound w/screen activity).

[1Roadrunner]

CPU Fan recently (this week) started staying on constantly (louder, more noticable). It doesn't cycle down to a lower speed/lower audible/quieter mode/speed.  Have tried shut-down, reboot, etc... to no avail. Last night applied vacuum hose to back of CPU at fan opening (while CPU was turned off). Re-started and fan ran quiet for a few min.s, but then resumed it's louder audible operation. It also started audibly surging to a higher/louder speed when any activity is occurring on the monitor screen (i.e. opening and closing websites, etc...).

I'm concerned that something might be wrong (or going wrong) with the CPU, in particular that the fan is going out.

[Grzwacz]

Hello

I don't think you have to worry about thermal damage to the the CPU unless the fan fails. 

The processor fan will run faster if the CPU is ramping up to higher frequencies.

The fan could be going but check Task Manager and see if any process or group of processess is causing excessive CPU activity.

No excessive CPU use in Task Manager suggests you should replace the fan and/or heatsink. Excessive CPU activity means you have a problem with a process that is tied to a particular program or system process.

Could also be a thermal sensor on the motherboard is either seeing incorrect CPU temps or the CPU is, in fact getting hot.

Reset CMOS (remove motherboard battery) or reset BIOS to defaults to see if that helps. Pull the CR 2032 motherboard battery and let the system sit for about 10 minutes. Maybe replace the battery if you have not done this since the PC was bought.

Download free Speccy and check all component temps.

Grzy