I know someone else has just posted an almost identical problem to this, but I decided to start a new thread because I would like to get into detail about my situation. I recently bought a used Mini from eBay with these specs: Intel Core Duo 1.66 80gb HDD 2.4x Superdrive 2GB Ram (Kingston brand upon inspection, so it has been user modified at some point) While using the machine I noticed that the fan speed would rapidly increase while doing non-intensive tasks. The most common causes of this seems to be HDD access and scrolling the screen. The fan speed is not permanent and does slow down once said activity has stopped and the machine is idle again. It is very easy to trigger this action, the best way i've found is that if i open iTunes and then scroll up and down constantly using the mouse wheel the fan speed will go from 2000 to over 5000 in a matter of about 30 seconds. Again, once i stop it will slow down again. I don't think temperature is an issue as smcfancontrol reports the CPU temp at 35-40C. I have since swapped the HDD for a 120gb and that hasn't changed the problem so i don't think it is HDD related. I have checked the fan control cable and it is securely plugged in. Looking inside i can't see any other signs of wear or damage. The thing that bothers me most though (i can live with the sound because i used to use a home-built pc that sounded like a jet engine 24-7!!) is that i've now noticed that when the fan is at it's peak, the bluetooth will start to become unresponsive which is very irritating as i use an apple wireless mighty mouse and alu keyboard. I tried a full re-install of leopard which hasn't fixed the problem. I've also tried resetting the SMR (although i'm not sure i'm using the correct procedure) and resetting the PRAM and neither has made a difference. Out of desperation I tried installing Windows XP via Bootcamp to see if it showed the same behaviour. In windows the problem is even worse with the fan running loud constantly and both mouse and keyboard being very unresponsive even when the machine is idle. So I would like to see if any of the experts here have any suggestions. I have no objection to taking the casing off again to check any components. I would take this to an apple store, but the nearest one is over 200 miles away. Any help is very much appreciated.