the CPU fan is DC type fan with magnets inside the fan. any rotating coil inside a magnetic field produces emf. The fans have also speed governors in the form of solid state devices. QuietMan meant and indicated the damage meted by the solid state components. Here the voltage is coming from inside without any external voltage applied. This definitely a case for serious consideration.
The photo showed by Pasan is a case of mechanical damage probably due to some obstacle while blowing vacuum cleaner.