Does it happen with your rMBP? Mine is a mid-2012 15" model.. the room has to be completely silent. As soon as I turn on the keyboard backlight, a static sound starts.. it sounds just like white noise. Does this happen with yours? I have this laptop since almost launch day and never noticed that.. fact is, I almost never used the keyboard backlight either so I don't know if it was always there or not. Try to get close to the keyboard with your ear if you don't hear it at first.