Why does my laptop sometimes make a sound as though it's typing, even when I'm not touching it?

I have an Advent laptop and it confuses me.. it makes me jump when it makes this sound that I can only describe as the sound made by someone typing really quickly. It seems to be coming from the keyboard or the parts underneath the keyboard.. not the speakers. As I highly doubt my laptop is haunted by a typing ghost, is there any explanation for this?