It could be the PSU. A tech would use a microphone (and possible an oscilloscope if he's older and unable to hear that high frequency sound) to find out where it comes from.
If they can't find it, return that laptop. it should be silent.
I am experiencing a subtle but irritating high pitch noise from my laptop, Fujitsu Lifebook E782.
The noise is not that high in volume but is quite annoying, since it is on a high pitch and almost constant. It is mainly there when I am browsing the net.
I have had a guy from Fujitsu to come over, and he concluded that it was not the harddisk nor was it the fan. He then changed the motherboard, but that has not solved the problem either. He said he will get back to me, but I honestly don't think he can do anything.
So I wanted to know if anybody else has faced a similar problem and have any kind of solutions..?