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GPU fan speed variation after replacing stock fans with new ones

Jul 13, 2016
1,029 (0.59/day)
Processor Ryzen 5800X
Motherboard ASRock X570 Taichi
Cooling Le Grand Macho
Memory 32GB DDR4 3600 CL16
Video Card(s) EVGA 1080 Ti
Storage Too much
Display(s) Acer 144Hz 1440p IPS 27"
Case Thermaltake Core X9
Audio Device(s) JDS labs The Element II, Dan Clark Audio Aeon II
Power Supply EVGA 850w P2
Mouse G305
Keyboard iGK64 w/ 30n optical switches
I recently replaced my GTX 1080 Ti's fans with new ones of the exact same model. The small problem I'm having is that when running under load the fan speed seems to oscillate.

For example, the card tops out at around 75c. Just sitting at that temp I can hear the fans slowing down and speeding up. Now it's not sudden or jarring, it's gradual but obvious.

I tried opening up afterburner and increasing the speed and it exhibits the same behavior at 70%+ speeds. At 75c it's running at 64% RPM.

Are these replacement fans defective?