Loudest Animal
Blue whales' low-frequency pulses are as loud as 188 decibels—louder than a jet engine—and can be detected more than 500 miles away (underwater).

On land, the loudest animals are howler monkeys, whose howl can be heard three miles away.

http://nationalzoo.si.edu/Animals/AnimalRecords/

My neighbors might just put my three parrots in the running for 'loudest' animals, but we can only hear them up to a few blocks away. :P