This is a problem I've had before on an old HP laptop. Now I have a Lenovo Z470. These are the keys I mean:
They seem to be capacitive buttons. When I press volume down for example, the volume goes all the way down and it keeps trying to go down (as if I'd kept pressing the key). Same thing happens for volume up and mute. I press ESC and it stops.
This does not happen if I use FN+DOWN (volume down) for example. So I'm guessing it's driver issues.
I found this, but it's really old and I've tried finding the code he's referring to but I couldn't: http://ubuntuforums.org/showthread.php?t=974723