"In space, no one can hear you scream." That was just an outdated, obsolete way of thinking. For advanced races in interstellar space, there were ways that one could hear sound. One of the methods used was psychic transmission, where you did not listen directly to sound but the mental thoughts of another.
While the pirate ships were all running away from the planet, the mysterious lullaby they made was broadcast even louder. For others, the lullaby sounded no different than odd melodious squeaking. For the Ultralisk, however, it was a soothing voice, like that of an angel even. It was a method the pirates had managed to devise in order to appear invisible.
*Thump! Crush!*
