I took the 8800GTX out and put in a Radeon 7000 PCI card. Still got the buzz. It ramped up when I OC'ed (stock is 266FSB) but it was still noticeable at stock. Also, whenever I did something processor intensive, like Orthos, the buzzing went crazy (including launching a 3D app). So I'm pretty sure it's not the 8800GTX.
Plus, I use to have a Striker Extreme with a different 8800GTX -- no buzzing (that I noticed). So if there were, this is completely different and unacceptable.