Cow bells in the engine

Has anyone else noticed this sound at idle speed, hot engine (2.0FSI GTI), if you stand outside your car you can hear what sounds like ringing bells, chriplike resonance. Seems to to coming from the area right near the alternator. Of course it doesn't do it all the time. Noticed it in my car, and a friend's GTI too.
I've recorded it with my cell phone voice recorded, sounds louder than it actually is in person See WAV link here, this sound can be heard starting at about the 4 second mark onward.

Chirp.wav sound file

Anyone else hears this? What is it??

Thanks