I see no problem with that. "Writing class" type thinking tends to make you think that everything has to be perfectly understood or you've failed. In fact,t that is far from the case. An excellent example is "Naked Lunch", in which Burroughs repeatedly refers to things throughout the book that are unexplained (candiru is one I happen to recall), sometimes explaining them halfway through. What does the reader do? Thow up his hands and go back to Herman Wouk? Fall into a frothing fit of confusion? No, you sort of read over it unless you're hopelessly anal.
Another example I can think of is William Gibson using the word "chilango". No explanation. Small percentage of his readers are going to know that's a person from Mexico City...but so what? What if it meant pigmies or samurai?
I've read a lot of things that mentioned songs I don't know. Who cares? And who cares if it's peppy or gloomy or whatever? One possible effect of this is to convey a certain hipness...it can actually raise confidence in the writer or narrator. Ross Thomas, for one, often writes about Europe and never describes the buildings or monuments. He just sort of "assumes" you know what they look like. After all, we're men of the world here, non?
Plus, those who DO know the song or what the facade of St. Sofia look like, get a special feeling from this. And they know you're one of them.
Obviously I'm overstating slightly something that is a subtle thing. What is important is this: you don't sell books by sticking to the ABC's. Don't be afraid to screw around a little.
And in this specific case, if that's your song, call it out. Don't worry if every person in the world is aware of it.
