If you like mariachi then you will like this video. If you don't like mariachi then you will like this video for another reason.
When crowds hit the higher end of the spectrum Disney makes adjustments. Normally the mariachi band is found inside of the Mexico Pavilion. They typically play by the wall in between the entrance to the San Angel Inn and the Grand Fiesta Tour. However, when the crowds grow more space is needed to expand the line for the tour. When this happens the mariachi band moves outside by the stairs (as seen in this video).
I could see how this could be an issue in the summer. I can imagine it would be tough playing in 90+ degree heat and brutal humidity with no shade. Good times!
You can see the video here.