I believe its your power supply. And yes you can change video cards and have your PS start doing it due to the fact that the load has now changed on your PS. I'm not saying your PS is overloaded by any means, its just that sometimes a change in hardware causes the load to change enough that the coils in the PS suddenly whine when they didn't before with a different load. I've had 2 GTX 780 ACX cards and one GTX 780 Classified card and they don't whine, however my previous Seasonic 700w PS did whine some in certain circumstances with the GTX 780 and didn't with the GTX 670 I had prior to it. I recently changed to a Seasonic X1050w and the whine has gone even with the same video card that was causing whining with the Seasonic 700w.