I worked there a few years back, and each limo originally had its own soundtrack. As mentioned, this has changed a bit over the years. I have a rather strange, but funny story connected to this, though.
One way for the cast members working at unload to tell how well we are doing is by the music. If things are going smoothly (meaning the trains aren't backing up in the brake area), you should hear the end of the song as the limo pulls into the unload area. I had a long shift one day, because the Sunset area was open late for a special event for the AK merchandise cast. During conventions, rather than move from position to position, we would just sign up for a spot and stay there all night. I chose unload, which was always a favorite spot. Earlier in the day, I was talking to a guest who clearly recognized me, but I couldn't immediately place this woman's face. She mentioned that "a lot had changed since we worked together." Then it hit me, it was one of my trainees from my Innoventions days, probably seven years back. Of course, the change was that "Jimmy" was now a transgendered female. It was a bit of a shock, but we chatted pleasantly for a moment before it was time for her party to ride, and off they went. That night, the weather turned nasty, so we didn't have very many CM's coming to ride, and we actually went down to only one train running. So for three hours, I got to listen to the end of "Dude Looks Like A Lady" over and over and over, which took on a very new meaning for me that night.