A childhood belief about ghosts

When I was really little my grandmother had this house that was up in the Catskill mountains in upstate New york. It was a nice house, but there was something wrong with the heater. (I believe it was the heater.) and whenever it came on it made this loud noise with almost like a whistle noise in the beginning. Anyways, for the longest time I would hear it and get scared. So my grandma would jokingly say, "Oh, that's just my friend who lives in there, you cant see him because he's a ghost! " I believed her, but as I got older I kind of found out on my own she was kidding. I look back and think of how silly it was to believe such a thing.