When MC "unpauses", does it act like it is unpaused, or does the UI stay "paused" but the music plays?
Not that I've ever seen such a thing, just curious. Also, you said your laptop's media keys "make a noise". Do you mean a system sound (ala a Macbook's volume up/down click)? I wonder if they have some crappily coded custom keyboard driver that is doing some misbehaving?
Try figuring out what process controls the media keys (or their auxiliary "fanciness") and kill it. Just to see if it might be related. There might be an update, or a simple reinstall might help, if so.
Another thing, that has
actually happened to me, now that I think about it... Does the HP have an IR sensor for an included remote (or optional maybe)?
My Macbook Pro does, of course. And when I take it under certain fluorescent lighting the media control goes nuts (I've found a few, CFLs and Tube-style, lamps that'll do it). Usually, it continuously turns the volume down until it hits minimum.
It isn't all or most lights that trigger it, and I think it might depend on the particular bulb age too, as it seems to go away (or come back, maybe). I know it has happened to me in my basement man-cave before, which has a CFL overhead, but not lately. Anyway... I'm throwing out ideas here. I didn't look up the laptop model myself, so...?
What audio output mode are you using? Could you try WASAPI - Event Style or ASIO (with the option to play silence on pause enabled)?
Is it possible your housemate is sitting in the other room with a remote and messing with you?
Back when it was easier to remote connect to most people's iTunes libraries with an iPhone (hardly anyone's were password protected, and if they were, they were often super-simple passwords), it was fun to do this when you'd go over to people's houses.
"Hey, can I get on your wifi?"
Sweet. (Check iTunes copies on the network... No password or same password?
Excellent. Save this for later.)