HP mini 2140 High frequency hissing/whirring

[vasalarcos]

Some days ago I noticed that my hp mini 2140 produces a high frequency hissing / whirring noise (I'n not native speaker, so not sure about the description - but the sound is like the highest frequency human can hear).
So I tested the thing and the results:
I have the hissing only when running from battery, and I can hear the hiss even in sleep mode, mode it's moderated in that case (only can be heard from the bottom of the laptop casing).
If i plug in the AC, then the sound disappears.

I have read many suggestions on the net.
What's your opinion? Can they repair it in the service, or every mini has this thing?

Anyway, what happened to the forum?

[miniproblem]

I found a similar instance with mine, it was charging and asleep. Immediately after unplugging the pwr cord, a buzzing occurred. I've determined by process of elimination that it's the internal cooling fan, spinning improperly due to a difference in current from when it's being charged or operating from the battery (the other option is the change in pwr supply AC to battery, causes the fan to spin-vibrate). It's annoying for sure, nothing a little percusive maintenance can't fix

[bver100]

I've got the same problem in my 2133, but it only happens after i wake up from sleep. It's quite loud, and people get disturbed =[

[vasalarcos]

Okay, thanks for your answers.
Actually I don't get the part when you said, that the hissing was caused by the internal fan.
Then how comes it is hissing even sleep mode? (though a little bit softer)