Let’s take a minute to talk about..
The bookshop
We all agree that she’s sentient just like the Bentley, right? She knows
Otherwise, how we can explain this?
Aziraphale just got (accidentally) discorporated, Shadwell is gone away (proud of his magic finger), so.. who has found the time to play some music?
The bookshop!
And not a random song: in the last phone call between Aziraphale and Crowley, he told him that he was with a 'friend', and the library decided to "answer" to this by making Crowley listen to "you're my best 'friend'".
[Just because, between them, the word "friend" covers a thousand shades of love, lust and fond. And glances. And physical contact.]
And I could continue with maaaaany other gif..
Surely the bookshop knows.. or feels.. this.