Noise machines are amazing. They can lull you to sleep. Animal sounds? I'm not sure about them. I love animals but if I heard a cow mooing in my place I might over-react. Or something. Here...the sounds of dust bunnies mating might be soothing...though.
The sound of a fan...good. Water trickling makes me want to pee. The sound of someone reading the bible ...now that might always put me to sleep.