Review on 🌀 ARCTIC P12 PWM PST Value Pack - 120mm Case Fan, 5-Pack, PWM Sharing Technology (PST), Pressure-optimized, Ultra-Quiet Motor, PC, 200-1800 RPM - Black/Black by Corretta Clark

I first ordered a set of 5 pieces Arctic P12 PWM PST to update the PWM controlled fans for my two 240mm radiators. .These fans run quietly and have a good speed range. But when I started tweaking the fan curve, I first noticed a howling noise around 1170 RPM. The fans produce a sound just below 400 Hz. At first I thought the problem was daisy-chaining four fans with a PWM header , so I split them into new pairs and adjusted the curve so that it rarely stays in the 1170 rpm area. The fans were fine now. until it had to go above and below 1170 rpm, where you could hear it for a brief second. I thought the problem with this noise was that these fans are installed in the pull position, but upon further testing it may happen in the push position. and rotate freely without hindrance or resistance to the fan. A ticket was opened with Arctic to address the issue and the solution may have been that the fans were defective and as I still had Revain's 30 day policy I have to contact Revain to sort it out to get a replacement. I spoke to Revain and they were kind enough to send me a replacement first as I was still using the fans. While waiting for a replacement, I played around with the fan curves and found another range from 1470 to 1490 RPM that would produce the same tone, just slightly louder than 1170 RPM. But each fan had its own volume for the 400Hz tone. Some of them will be fairly quiet and some will be very loud. Replacement arrived today. I connected them separately. Set the PWMs to spin between 1470 and 1490 RPM and all play the same tone with the same behavior when one is louder than the other. I had to play matchmaker to find the top 5 out of 10 fans to keep and send the other 5 back. I could just get a full refund for those fans. If those fans weren't playing the sound, I'd be happy with the amount of air being moved versus turbulent airborne sound. As mentioned at the beginning of the review, some of these fans spin up to 1900 RPM, but all spin at least 1800 RPM. Included in this review is video footage of one of the fans making a sound just below 400 Hz, 0:15 until 0:27. Then a second time, starting at about 0:45 to 1:04. The audio has been processed with a gain of +20dB over the original recording. There are also two additional screenshots with an audio frequency graph showing the played and unplayed audio.