Monitor making noises

At random times my monitor will just start making a high pitched annyoying sound. Anyone know what the cause of this is and how to stop it?

its a common problem, my old one used to do it and my TV doesn it also. i read that its caused by "faulty" inductors. Nothing i learnt in my electrical and electronic engineering course said that inductors could cause noise so i dont see how it could be cause, however i have noticed a similar noise from units with high value capacitors; TV's and monitors also contain high value capacitors.
i dont know of any way to cure this problem, however my old TV also made the noise and i used to whack the side of it to make the noise go away for a short period of time (note, i DO NOT recomend this lol)