Guru Zim sounds right on the money, I think. Check where your incoming mail is being sent from, that'll probably solve your mystery. Wouldn't hurt to have someone in your time zone fire you off a test email to check, either, if that's not inconvenient. Okies, I'll hush now. Hopefully it's nothing serious at all!
"Look. Keep your grandparents offline. I can't stand the thought of my own sweet nan coming into a chatroom to be textually spanked by someone like me."
In doing a quick search it seems like it's most likely a sound card driver issue. Try both the HP provided driver and the driver/codec from Realtek's website to see if that helps. Seems a lot of people have fixed their problems that way.