Arctic P14 PWM - Strange Hum/Drone at certain RPM's

[fromage]

Hi All,

Thought I would just report a strange issues I'm getting with my Arctic P14's.

At certain RPM's the fans seem to do a strange pulse/drone/hum/whistle, I have tested it on the intake fans (no grill near) and also the exhaust fans (grill on/next to fan) and its the same on both.

40% - Quiet no Hum/drone/whistle
45% - Quiet no Hum/drone/whistle
50% - Quiet no Hum/drone/whistle
53% - Noticeable Hum/drone/whistle
55% - Quiet no Hum/drone/whistle
60% - Noticeable Hum/drone/whistle
63% - Quiet no Hum/drone/whistle
65% - Quiet no Hum/drone/whistle
68% - Quiet no Hum/drone/whistle
70% - Noticeable Hum/drone/whistle

Anyone else had something similar? Its just a little annoying even though when my computer is at idle they are at 40% or even if I set it manually at 60% its when they ramp up in response to some temps/load and the fans go past these these certain RPM's that make this weird noise.

 

[fromage]

Yeah the hum less than ideal if you have a normal fan curve as various temps it can sit at these annoying RPM's. I have got around it by having very steep/instant increases that bypass the various RPM's the hum occurs at rather a normal curve that gradually increases/decreases rpm