Sometimes, while my computer is running, it starts to beep.
The beeping only starts after several hours of user inactivity, and it ends when I press a key or move the mouse.
The beeps are not of a uniform length - there might be short beeps alongside long beeps. However I think that, on each beeping seizure, the beeps become longer and longer until they become continuous.
I think that the beeps are coming from the speaker inside the computer, as their sound is similar to the startup beep.
What can cause those beeps and how can I find what is causing them in my case?
OS: Windows 7 Ultimate, Service Pack 1
Processor (from System Properties window): Intel(R) Core(TM)2 Duo CPU E6550 @ 2.33GHz
(If some other data is needed then please ask and I will edit it in.)