I'm sure I've got it, but I don't want to spoil it for others who would like a chance to solve it. So, here's my answer:

(SPOILER)Yuffie hiding in the urn outside Turtle's Paradise?

Heaven = paradise
Chelonia = turtle
Madonna = noble or important woman

Yuffie is stealing the materia to return her family pride, and she hides in the urn outside "Chelonia's Heaven"

...maybe the song refers to a noise she makes from inside the urn?