This paper explores musical metadiegesis, or the containment of one musical persona within another, much as Hamlet contains a play within a play. Previously regarded by Claudia Gorbman (1987) as "sound pertaining to a secondary narrator," I expand to what metadiegesis refers and how examples are identified in both visual and non-visual media. Following relevant scholarship on musical diegeses, I study works that establish hierarchically ordered diegetic settings and their direct implications. Referencing research on expectation, persona, lyrical address, and narrativity, I propose three frames which inform a work's diegetic scope, encompassing audio effects, narrative signifiers, and listener-generated expectations. I apply these frameworks to various music, identifying metadiegetic elements in contemporary piano works, pop/rock songs, musical numbers, and various film scores. I conclude with further avenues of study this paper reveals, and ways in which it serves as a compatible addition to the rich field of established musical narrative studies.