Question CPU_FAN header possibly faulty?

[SmilingJim]

I have two CPU fans by Deepcool that have run with no issues for three years. They are placed either side of my Deepcool CPU heatsink. Lately one makes a weird whine whenever it spins up above idle speed.
The one that makes the noise is plugged into CPU_FAN. If I plug it into CPU_OPT its normal even when running high speed.

Tried:

1. Replacing fan.
2. Changed CPU fan setting to silent in Bios
3. Disconnecting all other fans and cables related to CPU fan headers and RGB.

Any ideas?

Z390 Aorus Ultra MB
x2 Deepcool RF120M fans
DeepCool GAMMAXX GT BK, CPU Air Cooler
3080 RTX Aorus Master GFX
x2 *GB G-Skill Mem
Corsair RM 750 Pro PS
Thermaltake Core P3 case

 

[Paperdoc]

MAYBE look at his detail. Most fan headers now can be set to use either Voltage Control Mode (aka DC Mode) required for 3-pin older fans, or to PWM Mode ideal for newer 4-pin fans. I expect your fans are 4-pin, so normally you would want the header they plug into to be set to PWM Mode.

You have both CPU_FAN and CPU_OPT headers on your board, and appear to get different results with this fan you inquire about. On MOST mobos those two are complete mirrors of each other and do exactly the same thing, so often you do NOT have separate screens to configure them in BIOS Setup. But look in you system and see whether there is a separate screen for CPU_OPT. For what you are trying, it should be configured exactly the same as CPU_FAN. BUT if it is NOT, that may be linked to the difference in performance. In particular , check that the settings are the same between these headers for:
1. Temperature Sensor to use - this should be the one inside the CPU chip, and NOT one on the mobo; and,
2. MODE setting should be PWM Mode, not Voltage or DC.