If you have been leaving your computer on for extended periods of time, some emit a high pitch tone. There are multiple causes 1) you are covering the fans and the computer is overheating. solutions for this: try not to set your laptop on a sofa or pillow. 2) This could be a warning tone for pc inactivity 3) A faulty setting in your BIOS: this is an easy fix. Boot your computer immediatly press or simply hold down the F8 key (some BIOS keys are different if this doesnt work also try F12). It's been a while since i've owned a laptop, and i dont remember the exact setting. But poke around in the BIOS, being careful not to change anything that doesnt look like it pertains to the tone in question, The setting controlling the tone should be well labeled. Something like Warning Tone or Alarm or something to that effect.
Hope this helps!
Rob C, January 2005