I am a single mom who just bought a 2006 Cobalt with only 29000 miles on itfor my son's first car. We just picked it up from the dealer last night and in driving it today noticed a high pitched squeal coming from under the hood. If you turn the key to the ACC position you hear it for moment and then once the car is running it is constant.Turning off the A/C does not make it go away. The service dept. changed the fuel injectors (which were recalled) out before we picked it up. I had another family member listened to it and he thought it might have something to do with the electronics. Any ideas as to what it might be?

 

Could be something like a bad relay or a short in the alternator, hard to tell without being there to pin point the noise.
Seeing as though you just bought it, Bring it back to the dealer and they should take care of you