Here is a screen shot:
I have a late 2009 iMac with the following hard drive: Capacity: 500.11 GB (500,107,862,016 bytes) Model: Hitachi HDT721050SLA360 Revision: ST0KA36E
This is happening nearly everyweek, usually overnight when there is nothing happening on it. When i come back in the morning the fan is spinning at over 6100 rpm. Normally it spins at around 1100 rpm.
What is causing this, and how can I fix it?