DespondentDaisy -- i too live alone and i too find myself subvocalizing. this is totally within the norm as long as the frequency with it does not occur continuiously.
I live with a pet, and i talk to the pet. I am still void of people in the room, but sometimes talking to oneself provides insight into a problem, this is simply the phenomena of 'thinking out loud' and i find it to be perfectly within social norms.