Yesterday, as I walked to my 2006 HHR I heard a noise, the car wasn't on but their was a noise coming from one of the speakers. It stopped for a few moments with the door open, then did it again once Instarted the car but stopped after a few seconds. The noise was loud enough for me to hear it before I open the door.

 

see if it does it with the radio off before you turn off the ignition

 

You said "one of the speakers". Would that be the left front? The one that the chimes go through?
You may have a warning chime/malfunction happening. Just a guess.

 

what type of noise was it?