When I first met my guinea pigs they weren't happy. They were mad at the world actually. The man I took them from said: " It's not like I gave them any attention" as if it was funny. Animal neglect is never funny and there are rescues everywhere to save animals but once you have bonded with your guinea pigs you should feel responsible for them for the rest of their lives.
Needless to say, I learned the sounds very quickly and with a soft voice and routine I have been able to make friends and calm the chattering.
I realized that the most important thing to do was give each little guy more space and time free from the small cage they were stuck in. I saw that they chose to cuddle together when they have plenty of space and less chattering. If you are experiencing a lot of chattering between your piggies you should make some major environmental changes and move everything around before you separate them.
Teeth Chattering: This is an aggressive vocalization that is a sign of an agitated or angry guinea pig. Teeth chattering is often accompanied by the guinea pig showing their teeth, which looks like a yawn, and it means "back off" or "stay away."
Hissing: Like teeth chattering, this is a sign of a guinea pig who's upset. It is just like the hissing noise that a cat or another kind of upset animal makes.