XFX Power Supply Pro Series 750 W Bronze - Making Weird Noise on IDLE

[litwicki24]

Hello. I have that PSU
XFX XXX Edition Pro Modularny 80Plus Bronze - 750W (P1-750X-XXB9)

http://www.morele.net/zasilacz-xfx-xxx-edition-pro-modularny-80plus-bronze-750w-p1-750x-xxb9-554274/

But when i am on idle i have that noise:
https://www.youtube.com/watch?v=oat-oipfIbY


I must RMA? or that is normal?
The noise is somewhat continous but disappears when the computer is under heavy load.