I remember when I was in preschool/daycare, my teacher would give us all cots at nap time, and play some sort of classical tape. Most of the other children in the class would fall asleep, but I was wide awake the whole time(much to the teacher's displeasure). I am not sure it would have a calming affect on my daughter, as she would have the same stubborn genes. When she was three and four months, and still using a rock n play to sleep in, she seemed to like the nature sounds better than the musical ones her mobile provided. The fisher price classical music is tinny anyways.
I might try the radio in the car, and see if it works.