As a grade-schooler in the late 1960’s or early seventies, my teacher read the class a mystery book/novel about a little girl who’d gone to stay with relatives. Possibly for the summer. She was mystified by a haunting voice that would sing a song again and again. I remember something about a swing and hollyhock flowers. I’m not sure but I think by the end of the story it turns out to be the ghost of her deceased Aunt who died as a child.