When booting your PC the fans on your PC are controlled by the BIOS and not the Fan software. Hence they will spin up based on those BIOS settings. To fix this boot into the BIOS and go to Monitor --> Q-Fan Configuration. And select the header(s) you are using. Ensure you are using the PWM Mode and set the CPU Fan Speed Lower Limit to the lowest value possible. Below is an example where the CPU Fans header is used.