High pitched noises are caused by something going very fast. This may be something as simple as air being forced through a narrow orifice or by fast moving materials such as plastic or metal touching another surface.
The simplest thing to try is vacuuming out the air intake and exit ports on your laptop. With a bit of luck this will dislodge any accumulated debris and give the air a clear path.
Hard drives do have fast moving parts in them and you can find out if this is the source of the noise by removing the access hatch on the underside of your laptop and listening to the drive. You can often locate the source of a noise by using the old car mechanics trick of holding a solid rod on the drive and sticking the other end in your ear.
Optical drives also move fast so check that you don't have a CD or DVD in your drive that is spinning up.
Failing that the noise is most likely caused by a fast moving fan such as the one on the CPU or the system fan that is cooling your laptop. To check that out you will have to remove the complete bottom cover of your laptop and listen for the source of the noise.
Those are my initial thoughts but you may get alternative suggestions from those forum members that have had some practical experience of high pitched noises in laptops.