Start mission 7 and reach Club Errera. Return to the hospital. Fly to one of the ledges below the normal entrance. You should see a green light at the correct ledge. Activate it and return to Club Errera. When you walk in, the song "Never Surrender" will be playing. To change the music again, return to your Falcon and fly to the roof of Club Errera. Activate the switch located there to hear the song "Siege of Madrigal" at Club Errera.