They used that song by La Banda Gorda ad-nauseum. Since the OP mentioned hearing "trabajando" as one of the words, that has to be the song.
The words are: dejen esos perros que sigan ladrando, eso es seņal de que estamos trabajando. The PLD took on that phrase as a motto during their campaign.
http://www.youtube.com/watch?v=xcBDCLw1RuE