Strange running footsteps

Tonight I an alone, except for my dog Shadow. My wife is staying with friends until she can get in her appointment with a knee specialist. I was sitting here reading E mail, Shadow zonked out on her pillow in the Dining room. Overhead I hear the heavy footfall of someone running down our longer upstairs hallway. Whatever it is sounds like it is barefoot or wearing socks. It does not sound like hard sole shoes. The running goes the length of the hall and stops. I would go investigate but I know I wouldn't find anything. For some reason I feel the runner was female. It's just my impression. There has been no further sound from the upstairs. The weather has taken a turn for the cooler today. The temperature did go to sixty today but its only about 50 now and with a light breeze blowing you need a light jacket to be comfortable. The sounds of walking are fairly common here but I think this is the first time I've heard running when there is no one here. I know its the house making the sounds; I just wish I could figure out how it does it. The footsteps, whether walking or running, are sequenchal and the sound moves in a particular direction. I have a hard time thinking pipes or boards would be so well ordered. Shadow was and still is asleep so I have no idea if the "running" would have gotten her attention or not. If it be spooks they should wait for Halloween.