Squeeking sound from the upper left Doesent go away

I´ve had my MacBook 1 month.
It´s MacBook 2,4ghz, 4gb RAM, smallest hard-drive

I had a shifting high and low squeaking sound from my mac in the upper left corner, then I took it to service and they changed hard-drive, the logic card, and the speakers.

Now i had my Mac 3 days since the service and already the same day that I got it bak the sound returned, but now the sound only start when I remove the power cable.

So when Im sitting without the power cable the sound is constant except of when the computer is working harder (like running disk scan) but as son as I put in the power cable it stops, well almost, if I put my ear close I can still hear the sound but much lower and not consistent.

The people at my service place have no idea what this sound is
Do any of you know?

I would request a new computer if I were you.

Not a bad idea, just spoke to apple and they said that if the problem isn't resolved after 3 times in service I can get a new one.