I have a longhair syrian who does the chirping noise. He is a rescue hamster (yes really) who had an abusive first home. He's a sweetie and doesn't bite, but sometimes he gets scared, and I've noticed that he'll do the chirping noise if he gets startled by a noise or if someone bumps the cage. I think he's just letting me know that he's upset, because usually all I have to do is pet him or say something to him and he'll stop. I know that on more than one occasion he has made the noise for no reason other than to solicit me for treats, so I'm sure it has more than one meaning.
