I'm trying to get my computer whisper quiet, but still have one obstacle to overcome. I have a single Noctua NF-12 120mm fan and a Corsair H60 liquid CPU cooler, all housed in a Fractal R4 silent case. This has helped cut down noise considerably, however I'm still hearing the fan motor noise pretty significantly as it's amplified by the chassis. It's at a specific frequency, so I'm worried that introducing that extra noise will cause me to artificially cut my mixes there. However, I have no idea how to eliminate it. The fan motor noise is definitely coming from the Noctua, as unplugging it makes the pc virtually silent. Also, it's brand new as I just got it to replace the stock Corsair fan that came with the cooler. I was also getting the motor noise with the Corsair fan. Finally, I've tried adding some rubber washers to the mounting screws but that didn't seem to help it at all. Is there anything else I can do? It's one of those deals that by itself, it isn't very loud, but just noticing it makes it extremely loud in my mind and drives me crazy!

My DAW is pretty quiet more or less. I'm at my my office computer right now and it's notably louder.  For my DAW build I shopped for recommended parts that were known to be quiet. And the case is the most important part of this. My case has dampening pads on the sides. The Fan on the processor is the only one you can hear if you listen or if you take the sides off. The Power supply is quiet and there's no other fans. I didn't have to use case fans because the case is way bigger than what is really needed. My RAM has these huge heat fins and all but one BU drive is SSD which are cool. So only the CPU fan and its on some speed control so never really ramps up with what I'm doing. 
I'd shop around for a quiet fan. Lot's of info on that on Computer forums. I use the NCIX forum for these type of questions.  http://forums.ncix.com/
 

It seems that your fan has been rated very quiet in the reviews at Newegg.  Don't know what's going on, maybe the RPM?
https://www.newegg.com/Pr...x?Item=N82E16835608004
 
Check this out... Installing An Ultra-Quiet Fan
http://www.tomshardware.c...rformance,3435-16.html

See this thread I posted about how I got rid of Corsair cooler noise.
 
http://forum.cakewalk.com...ad-Quiet-m3562802.aspx

I put tons of effort into making the silent computer say 7 years ago. It all ended with me giving up. Sure I got the noise levels down. But you get to a point where you start noticing EVERYTHING. I want the best performance possible and no noise.... I don't think it's possible even with today's tech. One will have to go.

M

It is hard to fight against physics laws, but it is possible to use them.
Good way to make something inaudible is defining the line what is inaudible for you in your environment and select proper components for that level. Making existing system quite can be challenging. Also be aware about numbers...
For example you have already replaced 3.2 mm/H20 H60 fan with at most 2.6 mm/H20 NF-12. That does not mean something can be overheated, Liquid coolers are normally targeting "over-clocking enthusiasts". You just need sufficient parameters for CPU in question (which you also have not specified). So, many be you can use even lower noise fan, down to ULN:
http://noctua.at/en/products/fan
But ULN is 0.6 mm/H20...
 
One thing to check: does the noise really comes from the motor? The air flow going throw case mesh can be louder then the motor. And usually cut in metal halls like in R4 are far from optimal. Try to keep the fan in hands outside of the case, does it produce the same sound? If not, that is not the motor. Can be vibration (put it on the case surface to check) or the mesh (brutal making a big hall on its place can help, there are grills to put there in case you worry children put fingers there).
 

Thanks for all the great tips! I'll try mounting the noctua externally and see if that improves anything, and also run some tests to try and isolate exactly what is causing the hum.

My solution was to put the system in the broom closet. My computer room is next to a broom closet out in the hall. So I drilled a hole and ran a pipe in between and the computer lives out there.

Don't use stock fans.  Go and get some quiet cooling fans for you computer and if you did not buy a PC case with insulation for dampening the sound, then get some PC insulation and take off both side panels and Velcro the padding inside.   You will need a fan regulator, but it should not get hot as you have the good quiet cooler fans.
 
I have two fans on the top, two fans on the bottom, two fans in the front of the case and two fans on the back.
 
Spend some money on your box as it has to work well for you.  The two at the top and in the front pull air. in  The two at the bottom and the back pull air out.

I have an extremely quiet PC (see specs below).
I replaced my harddrives with digital drives to remove vibration.
I have a Fractal case that still cause fan vibration noise until I put a heavy book on the top of it. That worked!
You can't hear the PC at all.