You shouldn't.The reason why, is because of coil whine, is it OK to turn off the PSU?
I am switching PSUs soon.
PSU: Corsair CX550(gray model)
It is not ideal, I am aware of that, but it shouldn't damage the psu in any meaningful way, especially since he is replacing it anyway.You shouldn't.
There's a reason why modern PC's have "standby" and we're not still using AT power supplies from 20 years ago.
Your BIOS and memory settings are maintained by the +5VSB rail while the PSU is in standby. Also, when you turn the PSU back on, the bulk cap has to fully charge before the PC can turn on again and this inrush of current can be stressful on the PSU.
It's probably a better idea to figure out why the PSU is making noise in standby. In the case of my daughter's PC, it's a particular USB hub.
Unplug USB devices to see if the coil whine changes or goes away. Also, the problem could be noise in the mains line itself. Plug the PC in different rooms (on different breakers, of course) to see if the noise goes away.
Honestly, while some coil whine is normal, it shouldn't be so loud that you can hear it without your head being right next to the PC. So if it's really THAT LOUD, you should just RMA the PSU.