Even speakers of English all sound different. We have accents, that are determined by where we grew up. An accent reveals somebody's origin quite clearly (as long as the person listening is familiar with it - I am often mistaken for an Australian by many Americans, for reasons I'm not sure of).
Whales, elephants and songbirds all have accents. We've now discovered that goats develop them, too. And I do sometimes wonder if dog barks vary regionally as well.
So much for the sounds animals make being just instinctive. If they were, then perhaps we would not have developed a sound-based language, but rather something else...gesture-based, perhaps.