I have HP dm3 laptop and windows 7 installed on it. There is some beep for a 0.5 seconds periodically. There is no regularity. I did not found nothing suspicious in evets log. There is nothing suspicious in processes running on a machine. There is also avg 2012 anitvirus installed. My question is, how can I trace who is sending that signal. Which software do I need for this purpose or which functions to use in c/c++/c# to write a program by myself. I know for sure that this sound comes from sound card and not from pc-speaker.
Try opening mixer (click speaker icon on the tray, and then mixer).
The window will expand to show a volume bar per each application using audio.
When the beep comes, you should be able to identify which application it is as its volume bar will go blueish for a period of beep.
note: if the beep goes under category 'system sound' then it will require more investigation. But let us deal step by step with the issue.