I have a 12U 19 inch rack built into my computer desk, and I have a couple of NASes in it (2x HPC-8316SA-55RB1). The 40mm fans in the included CRPS PSUs are loud, whiny, and rattly, all at the same time.
I replaced all 4 of them with Noctua NF-A4x20s, wired to run at full speed all the time. They still report their speed so the IPMI management interface doesn't consider the power supply fan to have failed, but the PSU can no longer control the fan's speed.
The PSUs don't run any hotter and I can't hear them now.
I have a used Eaton PW9130 UPS in the bottom of the rack. The 80mm (exhaust) and 60mm (inverter heatsink) fans were likewise louder than I'd like. I replaced them with Noctuas too, again wired to run at full speed all the time, and the UPS' Web/SNMP card confirms it's still no hotter than 30'C internally. I can't hear that now either.
Hilariously, the most critical fan, the original inverter heatsink fan, is a 2-pin fan, so it probably can't even detect when it has failed (unless it's detecting fan failure by monitoring current consumption). The original rear exhaust fan uses a locked rotor sensor rather than a tachometer, which required a bit of bodging to convince the UPS that it has not failed. Oh well.
I’ve also done a noctua fan replacement on my ups. My worry is that they are rated for lower airflow than the original fans they replaced. Have you checked whether it stays cool when running on battery?
It's a permanent double conversion UPS; it's always inverting. You could activate the "high efficiency" bypass mode to directly connect the input to the output in the presence of mains AC input, but this would also pass through disturbances like fluctuations, harmonics, and surges, so I don't have it enabled. This wastes about 80W in my setup but whatever. I'm not worried about the inverter temperature is the point I'm trying to make; but I was considering this when I did it, which is why they're wired to run at full speed all the time.
They just never last. Arctic fans perform really well especially for their price but they all seem to develop problems. I have probably bought about 15 different Arctic fans from the F and P range and none of them survived 5 years, most were dead or developed noise within 1-2 years. Noctua on the other hand the old 80mm fan from the early 2000s still works just fine and remains quiet. Noctua fans are crazy reliable, they cost more too but I would suspect over the life of the fan they end up similar priced or cheaper.
Arctic fans seem to last 10+ years for me. I haven't bought any recently though and I run them at 500 rpm or so, that's my strategy: many and large fans, running slowly.
while arctic make fairly good high performing fans for cheap their bearings/acoustics are kind of bad. i bought 5 of the original p12 max fans with the ball bearings. they all made a chirping noise at various rpms (even after getting 5 new ones from arctic). the new p12 pro fans perform great but around 1200 rpms the motor is very loud and annoying
really wish arctic would now focus on the acoustics of their fans because its there weakest point. i wouldnt mind spending a bit more per fan if the sound profile wasnt just straight terrible which personally theirs are to me at the moment
It's sometimes uneconomical from a cost-ratio perspective, but it is crucial to making datacenter-grade equipment actually useable at home.