Bests & Worsts Reviews from Amazon

I initially ordered one 5 pack of the Arctic P12 PWM PST to get up to date with PWM controlled fans for my two 240mm radiators. These fans spin smooth and have a nice RPM range. But as I started to setup the fan curve I noticed an whining sound initially around 1170 RPM. The fans would produce a tone just under 400 Hz. At first I thought it was an issue daisy chaining four fans to one PWM header so I separated them into new pairs and adjusting the curve so it would rarely stay in the 1170 RPM range the fans were now fine... until it needed to ramp above and below 1170 RPM where you would hear it for a brief second. I thought the problem with this tone being produced was these fans are installed in the pull position, but testing it further it can happen in the push position and freely spinning with no obstruction or resistance to the fan. A ticket was opened with Arctic to bring up the problem and the solution to it was possibly the fans were defective and since I was still in Amazon's 30 day policy I should contact Amazon to get replacements. I spoke with Amazon and they were nice enough to send me a replacement first since I was still using the fans. While I was waiting for the replacements I was playing with the fan curves and found another range between 1470 to 1490 RPM that would produce the same tone just a bit louder than 1170 RPM. But each fan had it's own loudness for the 400Hz tone. Some would be pretty quiet and some would be very loud. Today the replacements arrived. I plugged them in individually. Set the PWM so they spun around that 1470 to 1490 RPM range and they all produced the same tone with the same behavior that some were louder than others. I had to play matchmaker to find the 5 best of the 10 fans to keep and send back the other 5. I might just end up getting a complete refund for these fans. If these fans didn't produce the tone I would've been happy for the amount of air being moved around vs the turbulent air noise. As mentioned at the top of the review some of these fans spin up to 1900 RPM but they all at least spin at 1800 RPM. Included in this review is a video recording of one of the fans producing the tone just under 400 Hz that starts at 0:15 until 0:27. Then for a second time starting around 0:45 until 1:04. The audio was edited for a +20 dB gain from the original recording. There is also two additional screenshots of the audio frequency graph showing the tone being produced and the not.