Oh my word, oh my gosh, its a ding dong door bell. Probably battery operated with those big D type batteries pushed into the plastic housing.
This is the constant drip, drip, drip of water falling into a pool or container. I don't think I have heard it quite like this as it does sound a little loud. It would drive you crazy like this.
Do you remember the sound that exemplifies the early days of mobile phones. It is the sound of an incoming text message.