I'm sorry, I made an error in my previous posting. I spoke of how 3- and 4-pin FANS operate, and said your first post sounded like a 3-pin fan on a header with certain settings. In fact, your first post said the PUMP is the item whose speed you were quoting. THAT makes more sense.
On most AIO systems the PUMP is designed to run at full speed all the time. Control of CPU cooling is done solely by changing the speeds of the FANS on the rad. For this to work, the PUMP needs to be connected to a header that always supplies a full 12 VDC to it, whereas the FANS need to be plugged into a header that WILL control their speeds (in PWM Mode for a 4-pin rad fan) AND bases that control on the temperature measured inside the CPU chip by its built-in sensor. Normally that is the CPU_FAN or CPU_OPT header, and you have both, OP.
Your PUMP unit uses a "trick" common on many. It is wired just like a 3-pin fan. So when you plug it into a header operating in PWM Mode, it always runs full speed, exactly what you want. You have it plugged into the AIO_PUMP header, which is a great place. IF you set that header to PWM Mode it will operate always full speed as it is supposed to. But IF you set that header to "AUTO", it will test the item plugged in at every start-up by using PWM Mode signals to try to slow it down. If that does not work, (and it does not for your pump) it assumes the "fan" must be the older DC Mode type and changes its operation to DC Mode so it CAN slow down the Pump. That is exactly what the AIO designers did NOT want! You SHOULD set that AIO_PUMP header to PWM Mode.
Now, THAT is what gives you your original problem - noise when it runs full speed. That is NOT normal for that pump. Two items could cause that - air trapped in the pump is one. You can try to move it out of there. With your system running, pick up the whole case and turn it slowly to various angles to try to get the air inside the pump to a pump exit point so it can flow onwards to another place like the rad. If that doees not work you can contact the makers of the AIO system - their Tech Support people - and ask for their advice. MAYBE the pump actually is faulty, but trapped air is a common cause of this.