I'd be working in the cellar and hear the front door open and close, then footsteps on rug, hardwood, rug and hardwood again, all the way to the dining room. I'd go upstairs and nothing. This happened pretty frequently to me, and two other people who were here when I wasn't home. The kicker is the dog would look up too.
I fiqure it's the old lady that died here so I don't have to worry about showing her around.