# Strange hummin after installing 3 Noctua NF-P12 Redux



## codis79 (Jul 25, 2013)

So I decided to upgrade my cooling with 3 new Noctua NF-P12's. I've got one venting out the back, two pulling air in through a filter on the top, and two stock fans that came with my Cooler Master case pull in through a filter on the front. As far as cooling goes, my temps dropped 13c, so that was a victory. Unfortunately, there's now a strange pulsating hum coming from the case. It almost sounds like someone waving a tuning fork around. I've been trying to isolate it, and I'm about to start unplugging fans one by one, but I thought I should check to see if anyone has any thoughts and what could be causing this.


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## oscer1 (Jan 27, 2010)

I think I would turn fan on top the other way and see if it stops.


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## Bill_Bright (Dec 17, 2004)

No need to unplug fans. 

Try this. "Gently" press your finger on the center hub of each fan, one at a time, just for a second or two. This will momentarily slow down the rotation speed of the fan that will change the pitch of the sound that fan is making. You should then be able to pinpoint which fan is making the offending sound. 

The fan bearings could be bad, or maybe a screw or screws mounting the fan are loose. 

I do think having the top and back fans as exhaust, pulling heated air out, is the best orientation. Typically, the only time top fans are intakes is when they are used to blow air through water radiators. 

That is a lot of fans, BTW. While keeping the internal components cool is absolutely essential, getting them as cool as possible is not. That is, a CPU running at 25°C will not be more stable, have better performance, or live longer than a CPU running at 50°C.


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## codis79 (Jul 25, 2013)

Ok, figured it out. A friend mentioned that he had a similar problem because of the hexagonal holes cut into the vents (which mine has), so he suggested moving the fans very slightly. I moved one of the top fans maybe a cm over, and it stopped. Weirdest PC problem I've ever had, but it seems to be fixed.

Side note: True, the hardware doesn't have to be at 0c, but I got a little gung ho when I was building  Also, initially tried venting out the top as well, once with both and once staggered, but the intake option kept the temps lower overall, so I just went with it (and the filter on top catches almost everything but fine dust, which is easy to clean out).


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## Bill_Bright (Dec 17, 2004)

For sure, air molecules banging into vent holes in the case will make noise. Not sure how moving a fan over a CM would make a difference. It makes me think just retightening the screws might have done it. And are you sure it was a centimeter? I have never seen a case fan or a case that supported that much wiggle room. In fact, I'm surprised there's any wiggle room.


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## codis79 (Jul 25, 2013)

Bill_Bright said:


> For sure, air molecules banging into vent holes in the case will make noise. Not sure how moving a fan over a CM would make a difference. It makes me think just retightening the screws might have done it. And are you sure it was a centimeter? I have never seen a case fan or a case that supported that much wiggle room. In fact, I'm surprised there's any wiggle room.


Could have been a loose screw, but it sounded more like a tuning fork or very low whistle as opposed to a rattle or vibration. My case is a Cooler Master MasterBox MB311L. It has slots instead of just pre-drilled holes for all of the case fans so you can reposition them.


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## Bill_Bright (Dec 17, 2004)

Well, what's a tuning fork do? It vibrates. 

Thanks for that screen shot. Now I see how it could have been moved a centimeter, or quite a bit more. 

And case fans can spin pretty fast. Some well over 2000RPM which would make a 2000Hz vibrating tone. This is what 1000Hz tone sounds like (turn volume down). The link will step to 2K and higher if you let it run.


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