The loudest sound ever heard on Earth was the eruption of Krakatoa in 1883.
The Indonesian volcano ruptured the ear drums of sailors 40 miles away, and people 3,000 miles away reported it as “a distant roar of heavy guns.” To put that in perspective, it would be like sitting in Boston and hearing a noise that came all the way from Dublin.
(Source, Source 2)
I got a little story about this eruption! You know the painting of the man screaming? It was painted many believe by the artist in a representation of him seeing all the way in Europe parts of the ash cloud mixing with the Sunlight causing a giant horrifying red light. You can read about it here.