Koala's Grunt.

Koalas are cute, sleepy animal (they're awake only 4 hours a day) except during mating season, where they:

... morph into aggressive, smelly creatures that you'd never want to cuddle in a million years.

The grunts and bellows of amorous male koalas are so loud they can sometimes be heard several kilometres away.

Read more (and listen to the grunts!) here: Link