Product rating for Noctua Nf-A8 Pwm

Is the noise difference noticeable? How did you turn the fans (blow air in or out)? Would also like to replace the original ones from my DS1515+...

I mounted the fans in the same direction as the original fans. I thought this was airflow from front to back (i.e. blowing air out).
The noise difference is noticeable (purely subjective, no noise measurements) and the fan settings were set to "Silent" before and after. more