These cats are pretty expensive, and this video hasn't convinced me that a good coffee machine wouldn't be a much more satifying purchase. The noise is better for one thing.
I'm pretty sure it's wanting to eat them. My cat makes the same sound when looking out the window at the birds on the deck. I read about it in a book and it said something like "Cats make this sound while hunting." which makes no sense to me, since the point of hunting is to be quiet isn't it?
Basically I think it means: "I'm nice and totally not going to eat you. Look, I sound like Chewbacca, that's cool right? You wanna hang out and totally not get eaten. You can work on your ArTooDeeToo impression. And did I mention that I'm totally not gonna eat you?"