Our one month old only settles with the bathroom exhaust fan running

Discovered this by accident on Tuesday night. Nothing worked, I walked into the bathroom with her, switched on the exhaust fan, and she was asleep in two minutes. Since then, every evening, one of us stands in the bathroom doorway rocking her to the fan. How do we get this out of the bathroom? Phone recordings of the fan don't work as well. Is it the sound, the vibration, or just that the bathroom is dark and cool in this Pune heat?