Hi Tianyu8452‌,

CPU goes to CPU, Front goes to GPU and Top to Ambient. Then, the Fan on the front of the computer goes straight to the video cards.

Thank you very much for your guidance!

Have a good day!

Sent from Mail for Windows 10

While there is a fan on the CPU (either your fan-cooler or the fan on the liquid-cooler's radiator) you don't have any control over it (the system takes care of it).

While there is a fan on the GPU (video card) you don't normally have any control over it (the system, the video card, and/or the video card software takes care of it).

For the two fans I can control, I link them both to the CPU Sensor, which should be the temp of the CPU. When it rises, both fans should follow their curves and increase the air-flow thru the system. Cool air in the Front, and hot air out the Top (heat rises).

At least that is how I understand it to work. It works for me.

No, they shouldn't be loud.
 
Switch to Manual and then setup a nice up-hill Curve on each.

With Manual & Curve, you have basically the same cooling going on as Auto, except you have more control since you define the specific Curves (and Sensors) for each fan.

The only reason they will get louder is if you are doing something extensive and they need to speed-up to cool-off machine a bit.