Hi there! I liked the video GrayRodent posted:-) I wanted to mention that I've heard two different types of "duck" sounds from our chinchillas. The one that GrayRodent posted is heard less commonly from our chins, but we hear it when our younger one is asleep and having a dream, and sometimes, when he's lonely. For example, on his first night with us, he squeezed out of his cage when we were sleeping (he was small) and he woke us up with this sound (we found him under our bed). It was as if he was looking for his "real" family. Now, he only does this on occasion (mostly when he's dreaming with his eyes closed). Our slightly older chin has never made this sound.
The other type of "duck" sound is like a softer duck quacking (imagine a happy duck, playing in a pond or eating). Both of our chins make this sound when they're happy and saying hello to each other, or to us. I know this because we can talk back to them and they respond--it's really cute. (This sound is different than what others describe as a cooing sound.)
Lastly, there's a totally different barking sound that chins make, and you'll definitely recognize it as a distress signal. We've only heard it twice and it sounded like a prairie dog sounding the alarm to his herd (or whatever prairie dog families are called). Our chin made this sound both times when he heard a loud sound outside (i.e. a large delivery truck driving up our driveway).
When we bought our first chin, I remember researching and finding the different chin sounds on another website, but I can't remember where. I'm sure you'll find it if you keep searching. Have fun getting to know your chin.