Noise continues after PC is turned off

After I turn off the PC it continues to "run". There is no output to the monitor, the keyboard caps lock light is not on, and there is no light from the mouse but there is a rumbling/grinding, dull clicking sound that does not stop until I power off the PS. The problem doesn't start when the PS is powered on. Any suggestions?
 
Failing PSU fan with a short?

Try to isolate - I use a microphone and Audacity set to record on my laptop. Sometimes I rig a funnel on the mic (card stock and a rubber band) so I could use it like a probe.
 
Back