What you're hearing
A contented cat purring very close: a deep, soft, steady purr with no meows. Keep it right next to you, or move it across the room until it's just a warm rumble at the edge of hearing.
Add rain on the window for the Cat on your lap starting point, or a Sleeping dog from Animals. The sleep timer fades it out after 15 to 90 minutes. The purr was made with AI and is marked AI in the list.