Hey man there is definitely an issue with your specific PSU I have a Super Flower and it’s silent Han hardly hear it with my ear next to it yes it’s vaguely audible but being able to hear it with all the other fans turned off with the case closed would be impossible even if the computer was a open build you wouldn’t be able to hear it unless year ear was very close with everything else silent I have sensitive ears and I thought the fan was off at the beginning until I looked at the thing to my surprise the fan was spinning but hardly making a noise
Side Note I have the:
Super Flower SF-750F14EG(WH) Leadex II 750W