Question New fans make a... "spinny, humming" sound I can't describe

[cloudropis_1]

I completely replaced my PC's fans, a Noctua NF-P12 for my Hyper212 EVO and two NF-P14 as case fans. They seem to work great, but while idle they produce this humming sound unfortunately my mic can't pick up. Imagine trying to softly spell "A" with your mouth closed shut, vibrating the bones in your head. It's perfectly cyclical, like once a second, and it makes me feel like i'm developing tinnitus.
It's not rattling
While it is harmonious, I don't think it's case resonance. I had that too, which I've now fixed, and it was a different noise that overlapped with the one I need help with. By touching or applying pressure to different parts of my case the noise doesn't change, unlike the actual case resonance I fixed.
My CPU fan is going at 900RPM, while the case fans are going at 750 (they share the same header so I see them only as one with hwinfo).

Any tips?

 

[CountMike]

I completely replaced my PC's fans, a Noctua NF-P12 for my Hyper212 EVO and two NF-P14 as case fans. They seem to work great, but while idle they produce this humming sound unfortunately my mic can't pick up. Imagine trying to softly spell "A" with your mouth closed shut, vibrating the bones in your head. It's perfectly cyclical, like once a second, and it makes me feel like i'm developing tinnitus.
It's not rattling
While it is harmonious, I don't think it's case resonance. I had that too, which I've now fixed, and it was a different noise that overlapped with the one I need help with. By touching or applying pressure to different parts of my case the noise doesn't change, unlike the actual case resonance I fixed.
My CPU fan is going at 900RPM, while the case fans are going at 750 (they share the same header so I see them only as one with hwinfo).

Any tips?

Typical Noctua, need to play with fan speed curves in BIOS.

 

[cloudropis_1]

Typical Noctua, need to play with fan speed curves in BIOS.

Guess I'll have to either raise or lower the idle temps. I actually prefer the noise when under load, at least it's consistent "PC is working hard" medium level noise with no moodswings.
Right now I get 35-37c in idle, is this low enough to let me slow down idle RPMs further? I honestly never cared about this stuff until this hardware change, and googling I see most people keep like 700-800 RPM at idle, do correct me if i'm wrong

EDIT also, do you know what exactly is the cause? Like, is it resonance vibrations, just the noise of the air, or what? If you can link some threads about this issue, since you make it sound like it's common, that would be cool too

 

[Lafong]

Right now I get 35-37c in idle, is this low enough to let me slow down idle RPMs further? I honestly never cared about this stuff until this hardware change, and googling I see most people keep like 700-800 RPM at idle, do correct me if i'm wrong

I've got 1 fan on CPU, one intake, one exhaust.

All 120mm Noctuas. All controlled by the BIOS settings to spin at near constant speeds...CPU 800; intake and exhaust at 500.

My idle temps are in the low to mid 30s in a fairly warm room.

I'd say you are fine turning your fans down or up a bit to eliminate that noise. I've never noticed it on my Noctuas (two NF-F12 and one A series.)

They will probably become audible as they go above 1000, but may not have the annoying noise at that level.