What you're hearing
A steady electric fan on its low setting in a quiet room: smooth airflow, no clicks or rattles. For many people it's the sound of sleep, and here it keeps going without the draught.
Add rain on the window, or brown noise underneath for more depth; the Lights out starting point puts it behind you, with someone asleep beside you and rain on the window. There's also an Air conditioner in Home. The sleep timer fades everything out after 15 to 90 minutes. The fan was made with AI and is marked AI in the list.