There are too many factors involved here. How loud the whine is, is relative, and also it greatly depends on the model of the video card. On a few of mine, it ranges from no noise at all, or barely audible. On others, there is obvious whine, to squealing. I also noticed that when the mining application stops, it also stops squealing.
Have you guys noticed any difference between miners? cgminer for one makes one of my 5870s whine quite audibly. phoenix not so much as a peep. There seems to be also a good 40w difference on power consumption. Yet the throughput seems largely unaffected. I run with water so not too much fan noise to cover the whine, but I bet one could hear this whine despite the fan noise of stock cooling!
So the real question is why don't the other cards whine?
Does this have anything to do with too low voltage(11.6v measured from whining card's power cable connector)? Can my caps blow up?