RainKindle is right - it's so bewildering when you first get them, but after a while, you just seem to know, somehow. I've had mine 2 months now and am fairly confident I know what they mean with their noises and the way they act - they've even started banging their bowls together when they think it's dinner time!
As for unhappy noises - I'm sure other people will say this too but the worst thing is if they don't make any noise, and don't move at all - Jerry used to get like that a lot if he heard any noise he didn't recognise because he's a big scaredypig
He's calmed a lot now though - one thing they both do is make a noise a little like a pigeon when they're confused, like a "what's that?" noise, which is usually brought on by the doorbell ringing or someone coughing/sneezing!
I know everyone says this, but just give them time - Ben and Jerry are so different now to how they were two months ago - they run to me when they see me, wheek for their dinner, and are so laid back they will happily lay on their sides in their cage and go to sleep (before they didn't seem to sleep so happily, they were practically standing up, on edge, all the time).
Good luck!