Yesterday (6-August-2014) strange sounds were heard from Herðubreið (Wikpedia link). It is unclear what is creating this sounds, it was first thought that a avalanche had taken place, that however doesn’t seems to be the case. Some have suggested a land-slide or rock-slide might have taken place. That has not been confirmed at the time of writing of this article. What might have happened, if anything did happen in Herðubreið is currently unknown and might remains so for a while longer.
Icelandic news about this
Snjóflóð féll í Herðubreið í gær (Vísir.is)
Óútskýrðar drunur frá Herðubreið (Vísir.is)