The reason fans spin up in any computer is that the temperature of the CPU, GPU, or both is rising and more cooling is needed ...
Your PC will have default fan settings, telling them how fast they should spin at any given temperature value. These are known as fan curves as the higher the temperature of your PC or specific ...
Are you using any additional case fans other than the 2x140mm on the front that came with the case? I’ve personally found that you don’t really have to concern yourself much with the operating curves ...