The loudest sound ever created would be a volcano. Volcano Krakatoa near Sumatra & Java exploded on 27 August 1883. Heard over 1/13th of the surface of the globe. Sent rocks 34 miles into the sky & took 10 days for the dust to settle. 26 times the power of the H bomb. Still only a fifth part of the explosion from Santorini in 1628 BC of the Aegean Sea.
Not sure, but have you seen the articles about teen-y Pop Idol Gareth Gates' fans being the loudest ever? - apparently they were recorded cheering for him at over 100 decibels, the level of a jumbo jet engine at take off! hard to imagine a sound even more annoying than his singing....