The more likely explanation for why you hear it in some locations and head orientations, is that the volume is right on the threshold of your ability to hear it. By turning you head, or obstructing the direct path, it drops below your sensitivity threshold. I have a ticking wristwatch that demonstrates this effect very well.
That could be the case sometimes but not usually for high frequency whines. They're can be pretty loud and annoying, and they fade in and out simply by moving - not turning - your head.
