Weird laptop overheating problem

My laptop (HP Pavilion g6) keeps overheating when left idle. As soon as I return to it, something that took up all the CPU stops within seconds (if I move my mouse to the bottom of the screen so that the task bar comes up, it lags while doing so, but that lag goes away in a few seconds), and according to SpeedFan, my GPU and some "Temp1" (which I assume is the CPU) are around 80 degrees and it immediately starts dropping when I move my mouse or do something on the computer.

Could it be a virus scan? I have Microsoft Defender. I haven't noticed any idle scan or anything like that on it, though. I have scanned the system for viruses multiple times and it has come up empty.

System specs:
OS: Windows 7 Home Premium SP1 64bit
CPU: AMD A8-4500M 1.9GHz Quadcore
GPU: AMD Radeon HD 7640G + 7670M Dual Graphics
RAM: 8Gb
HDD: Western Digital 7200rpm 1TB (iirc)

I have my laptop raised above the table a bit, since it has cooling problems even without anything running.