Hi,
I also encountered this problem, mostly when I undervolted the CPU and GPU. I did undervolt to minimize the noise of cooling fans, but the laptop showed this issue.
When the CPU fan was between 60°C and 65°C the fan ramp up to full speed. I made searches on the net and discovered a tool which help showing what happens in the Embedded Controller, and I managed to see that when the CPU Fan receives the order to put himself in state 2 the fan goes to full speed. More the CPU is hot higher the state of the fan is, on state 3 the fan runs at 2600RPM on state 4 at 2900RMP, but on state 2 (between 60°C and 65°C) it goes to full speed.
I even RMAed my laptop, they changed the CPU fan and same problem, I sent it back they changed the motherboard but the problem remains.
We need to get in touch with someone who can transmit the message to ASUS Bios makers : there are problems, this and the gesture control non responding touchpad after resuming from sleep.