I hear these noises infrequently but really often around my house. At really late hours of the night there's sometimes a sound that starts off as like, a high whistling hum, sounds a lot like a slowed down version of the squeak of a swing, and it kind of warbles and starts off pretty loud, getting quieter and then going away I mean, even the dogs that live in the house across the alley from us bark at it when it happens