Could well be the GPU, the coil whine could be a result of the GPU acceleration in your browser.
Should it be happening all the time, though? I could understand when it's only getting pushed to the max, but this is constant and unbearable.
I think it could be coming from one of the capacitor on the MB.
Yeah, doing some Googling, this seems to be a common cause. Is there a way to test for that? Ugh, I hope it's not. The motherboard is one of the more difficult parts for me to replace if it's faulty.