System Speaker sounds while playing hl2?

[margaritaheaven]

Once I start playing Half life 2 after about 2 or 3 minutes every time I press the mouse down to fire or any key on the keyboard, the speaker in the computer beeps. IT IS VERY ANNOYING. I already mutted the pc speaker option in the volume control, but that didnt do anything.
I have it unplugged right now. But i need it plugged in cause if the computer overheats the speaker goes off and lets me know.
Someone PLease help!