This alpaca gave birth to her baby the day before this was taken, so she is very protective. Her owner is holding her baby in his arms, and she is trying to make sure he is ok, and also trying to get him to put her baby down. Alpacas do make a noise, when alarmed or nervous. It sounds a bit like humming or perhaps whining. I thought you'd be interested in hearing it. I've not posted a video before, so if you have any problems with it, let me know in a comment or e-mail.
The photo is not that good--I was more concerned about picking up the sound, and just showing you how the mom was nuzzling her baby. I have posted good photos of the alpacas earlier, and will post more later.