"Moonlight Serenade"
From Tardis Wiki, the free Doctor Who reference
"Moonlight Serenade" was a song which Jack Harkness played while he was discussing "business" with Rose Tyler, whom he believed to be a Time Agent. (TV: The Empty Child) Jack later played it again for Rose while he was getting her and the Ninth Doctor on board[statement unclear], and then again when she was trying to get the Doctor to learn how to dance. (TV: The Doctor Dances)
Behind the scenes
In the real world, "Moonlight Serenade" would not be released until 1943, two years after this episode is set.