Fan revs when away from machine

Hello,

I have a question that bothers me. I have Windows 8.1 on my laptop. Here are the specs:

i7-4810
DVD burner
Plextor 512GB ssd
Kigston 60GB M-Sata (used as storage)
Windows 8.1

If I am using the computer it is fine and runs like normal. If I walk away from the machine for a few minutes the fan revs up and the HDD lights flash, like it is doing something in the background. If I sit down and open task manager it stops (can't see anything). The fan goes back to normal if I simply touch a key. Does this every day.

What is my computer doing?

Thanks.

Probably maintenance tasks running when idle, how long has this been going on. Look also in the start up items for any unnecessary programs running at start up and disable them.

Run Task manager minimized. Then when you get up, bring Task Manager up with CPU showing highest use at the top. System Idle should be around 80-100% if nothing intensive is running. I use Core Temp on my son's computer, so he can keep track if the CPU starts staying too high of a temp.