''Song Beneath the Song'' also known as Grey's Anatomy: The Music Event, is the eighteenth episode of the seventh season of the American television medical drama Grey's Anatomy, and the one-hundred forty-fourth episode overall. It was named after a song by American singer Maria Taylor. Written by series creator Shonda Rhimes and directed by Tony Phelan, it premiered on ABC in the United States on March 31, 2011. It is the series's first musical episode, and features the cast performing songs previously featured within the program. It is accompanied by a soundtrack album, titled Grey's Anatomy: The Music Event, also released on March 31, 2011.

What's the best answer to this question: grey's anatomy musical episode did they really sing?
yes