A baby who cannot relax can be helped to do so by a variety of constant rhythmical stimuli. it will work if the trouble is some kind of general and diffuse irritability or tenseness which is preventing a tired baby relaxing into sleep. The burring sound of a fan or heater works excellently. So does the sound of a car engine.
If you were to share your workout playlist with the world, I guarantee there's stuff on there that wouldn't pass the cool test, and M2 helped in that way.