Question CPU Fan erratic, even though CPU is cool and fan replaced

[Ranen Mannin']

ASRock Z170 Pro4 mobo
i3-6100
Thermaltake 95W Gravity A2 CPU Cooler, 92mm 4-Pins PWM 1200~3500rpm Aluminum Extrusion CPU Cooling Fan
16 Gb DDR4 ram
PNY GeForce GTX 960 2 GB XLR8 Elite OC
Corsair CX450M PSU
Western Digital Caviar Blue 1 TB 3.5" 7200RPM Internal Hard Drive

Out of nowhere, I don't even believe with any updates, this build (my wife's PC that I put together) started acting up. No notable performance changes, but the CPU fan is spinning erratically, fast slow fast slow fast slow, WHIRRrrRRRRRrrrrrrRrRRRrrRRRRR... So of course I figure the stock fan it came with was acting up, perhaps the paste is old. I changed the paste, tried again. Nope. Updated drivers, for everything. Nope. Tried manually controlling the fan speed from the BIOS, it ignored me. Checked the heat on the CPU (and all other parts), and everything seems nice and cool. So, nope. So I buy a new fan, installed it half an hour ago... NOPE?!?! Still no change. When I check the logs for fan speed, its the CPU fan going up and down with speed at high rate. This occurs on startup, during idle, and for the entire time it is on, just not while sleeping or off.

I'm running out of ideas here. I've cleaned out dust, I've unplugged and replugged everything. Any ideas?

 

[white.a.drew]

ASRock Z170 Pro4 mobo
i3-6100
Thermaltake 95W Gravity A2 CPU Cooler, 92mm 4-Pins PWM 1200~3500rpm Aluminum Extrusion CPU Cooling Fan
16 Gb DDR4 ram
PNY GeForce GTX 960 2 GB XLR8 Elite OC
Corsair CX450M PSU
Western Digital Caviar Blue 1 TB 3.5" 7200RPM Internal Hard Drive

Out of nowhere, I don't even believe with any updates, this build (my wife's PC that I put together) started acting up. No notable performance changes, but the CPU fan is spinning erratically, fast slow fast slow fast slow, WHIRRrrRRRRRrrrrrrRrRRRrrRRRRR... So of course I figure the stock fan it came with was acting up, perhaps the paste is old. I changed the paste, tried again. Nope. Updated drivers, for everything. Nope. Tried manually controlling the fan speed from the BIOS, it ignored me. Checked the heat on the CPU (and all other parts), and everything seems nice and cool. So, nope. So I buy a new fan, installed it half an hour ago... NOPE?!?! Still no change. When I check the logs for fan speed, its the CPU fan going up and down with speed at high rate. This occurs on startup, during idle, and for the entire time it is on, just not while sleeping or off.

I'm running out of ideas here. I've cleaned out dust, I've unplugged and replugged everything. Any ideas?

You need to adjust your fan curve ratio in bios, it's probably set wacky

 

[Ranen Mannin']

You need to adjust your fan curve ratio in bios, it's probably set wacky

Tried manually controlling the fan speed from the BIOS, it ignored me.

Did that, no change.

 

[Paperdoc]

The way a fan responds to temperature changes is not completely smooth. Instead most are set up to jump from one speed to another when the temperature changes enough. You may have just happened to land at a normal operating temperature just on the boundary between two speed steps, so it keeps changing back and forth. NOT a problem, but can be annoying.

Try this. Go into fan configuration for the CPU_FAN header where the fan is plugged in (see manual p. 72). In the CPU Fan Setting note what temperature you are running when this happens. In the menu choose the set a Custom "fan curve". Find the temperature where this is happening, and change the temperature setting (up or down) where the fan speed is supposed to change. Use the Esc key to back out to the Main Menu, then click on Exit at the top menu far right. On the Exit Screen (p. 78) choose Save Changes and Exit to save your new settings and reboot.

 

[Ranen Mannin']

Try this. Go into fan configuration for the CPU_FAN header where the fan is plugged in (see manual p. 72). In the CPU Fan Setting note what temperature you are running when this happens. In the menu choose the set a Custom "fan curve". Find the temperature where this is happening, and change the temperature setting (up or down) where the fan speed is supposed to change. Use the Esc key to back out to the Main Menu, then click on Exit at the top menu far right. On the Exit Screen (p. 78) choose Save Changes and Exit to save your new settings and reboot.

I have done this in the BIOS, it does not respond to my configurations. I suspected that I goofed by not saving it or something, so I did it three times. No change. It's at a nice 30C idle temperature. I would say that it isn't a problem, but it happens constantly, for a month or two now. It is super obnoxious, regardless of the technical issues it is involved with.

I'll do more investigating, and see what I'm missing here.

 

[Paperdoc]

Exactly where on the mobo is this fan plugged in? It should be on the CPU_FAN1 header near the CPU and right next to the RAM slots. See manual p. 6, item 8.

 

[Ranen Mannin']

Exactly where on the mobo is this fan plugged in? It should be on the CPU_FAN1 header near the CPU and right next to the RAM slots. See manual p. 6, item 8.

Yep, plugged in correctly. 4pin to 4pin, correct wattage, compatible sockets, etc.