Original post by: koppie007 ,
When you leave it off for a while (6 hours - 1 day) and then turn it on, does the fan still make a lot of noise ? If yes, probably the sensor is not working correctly anymore or the heatsink is not making (good) contact with the CPU/GPU. You replaced the thermal paste for both, right? And make sure you don’t use too much thermal paste, this will seriously increase heat, as it will isolate instead conduct.