I'm still not sure what it is. Both the case fan and the processor fan seem to be running fine. The only thing I can think of is that the chip is no longer making good contact with the heat sink, but I can't really SEE that, as the heat sink is huge. Anyone in Arlington/DC have thermal paste handy?
Otherwise, my parents recently upgraded and I can pick up their old Compaq for the time being. I'm slowly convering over to Macs anyway, so I might just use the Windows box as a playback device before too long and control it remotely. I'm putting my drives in FW cases as well, so soon I won't have to worry about being tied down to a box. It's all about the data!