Continuous Beep while on screen saver

[posterce]

I have my lap top almost 3 years however today very strange thing happened,i usually leave my lap top running on desktop background while im out for a short period of time, and today i did the same thing.But when i came home there was very strange and loud Beeping sound almost my ears started to hurt,and as soon as i clicked my mouse the monitor turned on from the screen saver and the beeping stopped.Any idea what might have caused this?Also nothing rly changed everything is working just fine but the sound was scary and rly loud.

P.S i have DELL midrange lap top connected to external monitor,mouse and keyboard.

 

[hang-the-9]

Could be low battery warning, or overheating warning. Or a program notification. Quite a few things. Did this happen once? If once, it's not an issue yet if everything else was working fine. Could also be that a keyboard key was pushed down.

 

[posterce]

Hm well it was plugged the whole time and the room was cool i doubt it was overheated from running on desktop only.And yes its happening the first time and the my lap top is with closed lid since im using external keyboard but there was no object or pushed button on the keyboard.And last for notification i had my League of Legends client running and someone has invited me for a game mby that was it,but the notfication for that is just i single sound i know how that sounds ,and its also coming from my speakers, however this sound was high pitched , continuous and it was coming form my lap top not from my speakers.