Loud female voice

A couple days ago, I was home with just my dog "Shadow". I had managed to sprain, strain or otherwise compromise my back between the shoulder blades and was taking it easy lying on the bed in the master bedroom with my dog beside me. I was reading a book and the house was very quiet. Suddenly with no forewarning a voice was very clearly heard coming from the rear stairs. It was loud, definitely feminine voice that said, "Yaup?" that's slang for "are you up?" I replied that I was and expected to see my wife appear. She didn't. Shadow heard it too as her ears went up and she was alert. I called back down the hall several times that I was "up" (even though I was lying down). Still no result. Very gingerly I did get up and make my way down the hall. No one anywhere. The back door was locked as my wife always locks up when leaving the house ( so do I, it's just a habit.) I called my wife who was down at her store and she simply stated it must be one of the "staff" checking up on me. This house was a rest home for many years before I bought it. Another strange thing is that my dog, though she seemed to hear the voice, did not react in her usual noisy manner. Only two females have a key to this house, my wife and my god daughter. My god daughter was in Virginia at the time and my wife was running her store roughly 10 miles from here (As the crow flies.) Old houses can be very interesting if they don't drive you nuts.