I also got a dud. I have the same electrical interference, can't hear it too much with headphones, but when I plug it into my home theater it is very loud and noticeable when there is no audio playing in between tracks or with music playing that is softer in volume.
I also had to ship this back to HP because the screen developed a weird black bar on the right side of display and repeated everything on the left side of screen, on the right side of black bar, as well as repeating the top across the whole bottom. Then about a week after that developed, the whole screen flickered and went dark, the backlight died and never came back.
I just got it back from HP yesterday, it only took them about three days total for shipping, repair and return. The screen is fine now, but the audio issue is still there, but it seems to be a little better.
I am concerned that this screen problem will happen again, since I don't abuse my computer and it hardly ever goes on the road with me, usually just sits on my desk. Hopefully it happens within the next 4 months, then my original warranty is up.
Let me know if you find anything out about the audio issue, I will do the same. Thanks, Brian