Had this problem for over a year now.. seems to go away during cold months. And is very noticeable during warmer seasons.
It's a very high pitched whiney, crackling noise that comes from the front right area of the cabin. At first thought you think it's the speaker, I've replaced the speaker, no change.
One odd ball thing is if I press the power button on the onstar module it will turn the noise off but then it starts right back up again, soooo annoying. I'm planning to rip apart the dash and disconnect the navi, onstar and then go from there.
I got a video of it.... anyone seen this before? I've been searching for answers for awhile now and had no luck
http://youtu.be/l5Btgn6cHuA