Susurraron comes from the verb susurrar, meaning "to whisper". It's a beautiful and evocative word that paints a vivid picture of soft, hushed sounds.
In the song, the lyrics say, "Mil violines en su voz susurraron un adiós" (A thousand violins in her voice whispered a goodbye). This personification of violins whispering creates a poignant and memorable image, making the farewell even more tender and sorrowful.