My mother is 81. She lives alone. For many years she has been hearing knocking on her house outside of her bedroom. It happens around 2-3am, and happens a couple times a week. She was convinced it was her next door neighbor. She since has moved across town and is hearing it again. She is convinced it's a new neighbor, but doesn't see the correlation. She installed cameras on the outside of her house in both places and nothing is there. Could this be a symptom of a health related problem?