I am very wary of elephants - they can be extremely unpredictable, especially if they have young or are a bull in musth (pronounced "must" it is the period in a male elephant's life when his testosterone soars and he is ready for breeding).
When I first visited Kenya as a child with my parents and my brother, we were charged by a bull elephant. I was only about five or six at the time, but I have never forgotten the incident such was the fear it engendered in me at the time! There is nothing like having several tonnes of angry elephant bearing down on you to make you only too aware of your own physical shortcomings! So I have given elephants a wide birth ever since!
Elephants are, nonetheless, fascinating creatures - highly intelligent, they form complex social groups. Thus, they have a range of strange and weird vocalisations as tends to be the way in nature that the more complex the social group, the more complex the vocalisaions that species employs - hyaenas being another great example.
Below are some excellent resources about African elephants: