I used to have a truck that I swore had the ghost of a dead baby in it. I used to get home late from my job as a dishwasher, and after I parked and was sitting in my driveway with the engine off, I would hear this really faint sound of a baby crying. Late at night when it was quiet, it used to make my arm hairs stand on end. I used to get home and hop out of the car in fear of hearing it.
One night I decided to sit there and just listen, try to pinpoint the sound. Eventually I discovered that it was indeed not a dead baby, but when I undid my seat buckle, the old spring of the seat belt retractor would slowly start pulling the belt in, creating a faint noise that sounded like wailing.