This would work if the elevator music was a never-repeating stream. With most elevator music, it's a few minutes of a "song" playing on repeat 24/7, so if you recorded a few repetitions of the "song", you'd probably see also repeated packets on the network.
If the music was repeating but the stream was different all the time, then steganography could be the reason :)
If the music was repeating but the stream was different all the time, then steganography could be the reason :)