X200 humming noise

[mt12345]

My X200 produces high pitch humming noise, the noise pauses when I press the keys or scroll web page.
It's not loud but should I be worried (is my Thinkpad dying?!) ?

[jaspen-meyer]

Can you identify where (on the machine) the humming is originating?
In some configurations the CPU can jump between power states and cause humming. Also the power supply, external to the machine, between the mains and the computer, can develop a humming sound.
CCFL inverters also hum.

[glossywhite]

Maybe it's trying to remember a song, but can't quite place the lyrics...