A new purchased chinchilla often makes use of that sound, because there's lots of strange noise in its new environment. However, during the time, when the chin gets used to its new home and gradually becomes tame, you will hear this sound rather rarely.

Chinchillas have a very sensitive ear. For instance, if a car door shuts somewhere from a distance, we human don't realize that noise, because we got used to it too much. However, a chinchilla may go in fear of that noise because it sounds so strange.

Occasionally, you can hear a chin barking while it is sleeping. Usually, it makes just a few croaky/hoarse shouts then. I am sure chins do dream! I think they sometimes even have nightmares.

The Short Alarm Call
If a chin gets shocked because of a sudden noise and cannot realize it at all, it tries to run away as fast as possible. Then it shouts of fear in a manner of a short call, which sounds like <<Hababababapp>>. That sounds very funny.

Fear and Pain
In extreme situations a shy and irritable chinchilla reacts through a loud and piercing scream. From a tame chin however you will hear this cry only extremely rarely.

Chins also make use of this cry in pain - for instance, if they have hurted themselves anywhere.