I for no apparent reason, my CPU began to make a fairly loud chattering noise, obviously based upon some sort of rotation. I opened the case and stopped the fan but the noise persists. There appears to be a cooling unit of sorts under the fan.
I also just replaced the video card, but the sound appears to be coming from the processor (And its not the fan)
Well, all three comments drove me to trouble shoot everything that moved with inside the case.
After disconnecting everything with power, I still heard the noise. I stuck my head in the box just to listed and isolate the noise. Eventually I found on the very bottom (underside, facing the bottom of the case) of the video card the cooling fan is exposed and a SATA cable from the HD was rubbing the exposed fan blade. I moved the errant cable and all was right with the world.
NVIDIA GeForce GTX 660 2048MB
Also, the system seems to be running a bit slower as well.