since a short time my iMac does a chirping noise.
The noise appears after a short period of use of the iMac.
Approximately after one hour.

The sound of the fans are normal.

Please, listen to the mp3 file and the noise.
I recorded it with the internal microphone.

The Power-Supply of the iMac was already changed by Apple
but it was no solution - the noise is still to hear.

Listen to it: "http://www.michael-meier.net/File.mp3.zip"