Crackling sound from speaker...?

This is odd... I'm getting an intermittent crackling sound from some speaker. I noticed it while driving and listening to the stereo the other day and it continued after I shut off the stereo. I was further confounded when I was working on my interior yesterday with the key not even in the ignition and it continued to make the sound.


It doesn't sound like it's coming from my stereo speakers. Does the OBC have a speaker somewhere that it uses for things like the audible tone for the speed warning? Any thoughts on what might cause this? Is there a common short in the system?

Thanks for your input.