About a month ago, I noticed a faint ticking coming from my case and decided to investigate. I discovered a ticking NF-S12B FLX that I had been using for an exhaust in my Fractal R3. Luckily, I had a an NF-P14 sitting idle. I rejiggered my setup so that that I now had two NF-P14s on my NH-D14 heatsink and moved the NF-P12 that came with my HSF to the exhaust position. All was well.

Now, I'm hearing a ticking again, and it's definitely coming from one of the 14cm P14s on the HSF. What's going on?? I never had any Noctua fan start ticking on me before, and now I've got two of them. I use a NZXT Sentry Mesh fan controller and almost always have it dialed down to 5v. Could I be damaging these fans in some way by running them at that voltage? The ticking goes away as I turn up the fan controller, but not until it gets to quite high RPMs.

My Nexus silent fan also emitted some ticking noise. But it went away. I maybe tapped it a few times. Don't know what actually helpet but try to tap/know/shake it to see if it helps.

Thank you for the suggestion. I'll try giving my ticking fans a good tapping and see if they get better. In the mean time, I've gone down to one fan (between the heatsinks) on my D14 and it doesn't make much difference in temps. I'm still hovering in the mid-60s under IBT w/AVX (4.5GHz, 1.3v), so I think I'll be fine with one fan.

I'm tempted to order some NF-F12s though. They look fun.

I should probably contact Noctua. I've heard they're pretty good about replacing defective fans.

If they are still under warranty (and since they are warrantied 6 years, they should !), Noctua will replace them without problem

I will avoid the NF-F12 PWM unless you plan to use it on a thick radiator..its noise is not really "musical"...overdesigned maybe ?

The NF-F12 is optimized for PWM use. Deployed as a PWM fan it is somewhat quieter than when it is used under voltage control. Even under voltage control, which is not optimal, most reviewers say it is fine under about 1100 rpm. How are you using your NF-F12?

Now it seems that the other P14 is also ticking. Much more quietly but it's there. Maybe they've always ticked but I haven't noticed it? I recently installed aftermarket GPU cooling; perhaps my stock graphics card has been drowning out the ticking of these P14s.

Could the fan controller be somehow responsible? I'm going to have to do some more investigating to get to the bottom of this.

EDIT: With all fans unplugged except one (a Nexus at 5v), I can actually hear a ticking coming from the fan controller itself. I think I may have found the source of the problem.

OK, now I know there's something weird going on electrically with my case or with the fan controller.

I was monkeying around with the fans, plugging and unplugging them, and accidentally touched some exposed y-splitter pins to the chassis. Sparkles! Computer stable though (of course it was on while I was doing this).

And suddenly all the ticking, which I'd started to notice was in fact coming from almost ALL the fans in my case, is gone.

I'm thinking it may be the ungrounded wiring in my apartment? Thankfully, we're moving July 1st to a place with modern wiring. If this is in fact the cause, hopefully it will never come back after that.

So far I've figured out for sure that the fans ticking is caused by something systemic, not the fans themselves.

I've tested under voltage control and under PWM control (motherboard and Zalman rheobus with PWM). In both case I found it accoustically inferior to the NF-P12 PWM...or other fans. I was expecting more from a such designed (and expensive) fan...
And since for me noise and accoustic are far more important than performances (since the temp are "ok"), I'll stuck with NF-P12 PWM for the moment, or Noiseblocker PL-PS

maybe the bearing is gone.

I tested both under PWM control only. At the lowest idle speed setting, the NF-P12 PWM was running at 280 rpm and the NF-F12 at 320 rpm. This reflects I guess that the NF-P12 has a top speed of 1300, and the NF-F12 1500 rpm. At these low speeds I couldn't detect any difference between in terms of noise. Upping the speeds to around 700 rpm also produced no difference between them at a distance of around 1 foot, 30 cm. However when I put my ear right next to the fans the NF-P12 was quiet; the NF-F12 produced what I would describe as a tone. When the ear was moved around 4 inches or 10cm away this tone disappeared. It may be a result of the Focused Flow features. So I agree with you to the extent that there is an acoustic difference between this two fans. However I don't think it will make any difference once they are in a system.

How to Oil a noisy fan:
viewtopic.php?p=541788#p541788

Not relevant to Noctuas, they have a sealed bearing.

Yes but does the F12 provide higher pressure and more airflow at that speed? It would be hard to test this but on their site they do suggest that the F12 is more tuned for pressure and less for silence then the P12.
http://noctua.at/main.php?show=which_fan_is_right_for_me&lng=en