I'm guessing it wasn't a big office building then. I always hear the music seeping in from the lobby of the building to my waiting area, which is what I mean maybe it was coming from a totally different office. (Like a radio or streaming music or something.)

In my experience, hallucinations can come and go really fast or last a while. It just depends on something I don't know what. If it was a hallucination then you might not have it again ever. Or you might. Or it might come back as something different. So, just anything I suspect I make a note somewhere that I can look back.