I have noticed that if I leave my computer at idle with no input for more than 15 minutes, the disk starts spinning with no apparent cause.
It is annoying if I want to put my headphones on and listen to music because it causes the music to skip. It's also annoying that my hard drive is
getting unnecessary wear and tear if I want to leave my computer on for a large download.
CPU: AMD Phenom II 955 C2 BE
Motherboard: MSI 790FX GD-70
RAM: 8GB Corsair Dominator DDR3 1600 @ 1066 9-9-9-24
Hard Drive: Seagate Barracuda 7200.12 1TB
PSU: Corsair TX750
It's probably your antivirus, windows indexing service, or background disk defragmenting. You'll need to disable each one individually to figure out which one. I'd start with the windows indexing service first as it's the least important of the three.