From the AWeb Site:
A new paper from Acta Zoologica (Natale et al. 2010) reports that the tadpole of Ceratophrys ornata makes distress calls underwater, the first example of any larva communicating by sound underwater, and the first known of any vertebrate larva to make sounds.
Tadpoles are able to make the calls as early as three days after hatching, and can do so both in the water and out of the water. It is not known how other tadpoles perceive the calls, but while C. ornata larvae are carnivorous towards tadpoles of other species, they do not consume conspecific tadpoles. To hear the sound, check out the two video clips in the associated BBC news story.