I know you are going to think I'm crazy, and I honestly thought it was a website pop-up the first time I heard it. But, if I have my headphones plugged in, and it's quiet, I can hear some radio station coming in and out. It's faint, but the sound of human voices is certainly there. I have one of the new MacBook Pros, and ever since I got it I have noticed the audio quality is not that great. I get a bit of a static hiss feedback, and an occasional very quiet, but high-pitched tone if I am wearing headphones. Before you say this guy is nuts, please take comfort in the fact that I'm not. This is the third time I've heard it now, and I thought I'd ask if anyone has any possible explanations or ever heard of anything like this?!