Any chance you got around to testing the D30 fans with setting them to a lower value?
And just to be sure, you mean the rather new D30 D-RGB fans and not the T30 (w/o RGB)?
Sorry I forgot to do this. To be clear, I am talking about the new D30 D-RGB. I have a 3 pack of them and a 3 pack of T30s. I will do the test today and report back.
UPDATE - Schnipp - You were right. My D30 RGB fan does the same thing yours does. At 0% PWM it goes to full speed (~2080 RPM). At 100% PWM, it also is at full speed. As I decrease the PWM value, the RPM drops in a very linear way. At 10% PWM, the speed is ~260 RPM. At 9% to 1% PWM, the RPM is 0. At 0% PWM it jumps back to max RPM.
I set the fan port for 25% PWM then shut down and rebooted the computer. When the fan gets power, it starts spinning. It sounds like it is speeding up, probably headed to max speed. Within 2 seconds, it slows back down to ~512 RPM which is the speed I get at 25% PWM. It seems that the Octo sends 12VDC to the fan about 2 seconds before it sends the PWM signal. Apologies for my earlier statement. I just never noticed it, I think because the fan never gets to full speed before the PWM signal takes over. I had to listen closely to hear it (the fan is not installed in my case, it's just sitting on top for now).
Other things to note about the D30 RGB - There are 30 LEDs in the fan, not 32 like Phanteks marketing says. Also, the LEDs are not individually addressable. They are arranged in 15 pairs of 2. If I set an RGBpx controller for 1 LED, 2 LEDs next to each other light up. If I set the controller to 2 LEDs, 4 LEDs light up. The pairs are arranged so that they progress in opposite directions from the first pair. Using a clock face as an example, if the first pair of LEDs are at 12 o'clock, the second pair are at 11 o'clock and 1 o'clock. The third pair are at 10 o'clock and 2 o'clock, etc. I don't know why Phanteks did this. DRGB LEDs are INDIVIDUALLY controllable so why pair them? Doing this will mess up RGB effects that progress from LED to LED. Also, to light all 30 LEDs, you set the RGBpx controller in Aquasuite to 15 LEDs. Now the port is driving 30 LEDs when it thinks it is driving 15 LEDs. This causes the current and power calculations to be wrong, so be careful with how many D30 fans you connect to an RGBpx port. If you connect 3 of them to 1 RGBpx port, that is 90 LEDs but you will set the RGB controller in Aquasuite to 45 LEDs. I read that Lion Li Uni-Fans and Infinity fans also have the LEDs paired, so Phanteks is not the only one doing this. I still don't understand why they paired the LEDs.
Here is the RPM vs PWM data for my D30 RGB fan.
Phanteks D30 RGB - RPM vs PWM.jpg