The same thing happened to me here, Richard! When I first bought this house, I heard the "Hello?", except that it sounded just like someone was at my door and didn't want to just walk in, so they said "hello" in the form of a question. I was busy putting things away and said "Yes?" and the voice kept saying "Hello?" and I kept answering "Yes?" until I grew impatient and went to the door, only to hear the ice cream truck.

Years ago, a (now) late senior friend of mine went to check up on another senior friend because she hadn't heard from her in a while. She knocked on the door and heard "Yes?" and my friend answered "It's me, Helen!". No answer. Helen knocked again and heard "Yes?" and again she yelled louder this time "It's me, Helen!" No answer. This happened a third time, so she thought she would go around to the back door and when she got there, she heard "Yes?", only this time she could see that it wasn't her friend who was saying it. There was a goat tied up in the back yard and it sounded just like it was answering "Yes?" every time Helen knocked on the door.

There are stalkers everywhere!