Two elephants have caught the attention of scientists by making sounds that are not made by elephants in the wild. It is thought that the elephants are trying to communicate - in one case an African elephant with an Asian elephant (they are genetically different and make different sounds), and in the other case an elephant imitates truck noises. Scientists are researching whether elephants in the wild also imitate other sounds they hear.
To read about these elephants, see here or here or here. You can listen to a recording of the truck imitation here or recordings of both unusual elephant calls here.