speed drops to minimum during the night/when away

[gerapa]

Hi, I hope you could help me with my rather strange problem;
 

My uTorrent downloads usualy with 500kps (fine with me) but when I leave my computer on and downloading, but I am not there (for example during the night), download speed drops to almost zero (someitmes actual zero). As soon as I just move the mouse or turn on the screen it jumps back to 500.

I have prevent standby box checked, and my computer doesnt go to sleep or shuts down for sure. 

 

I use 2.2.1 but had exactly the same problem with any other version including newest one.

 

Please help!

 

Thank you