Believe it or not, different sounds can mean different things.
Loud Chattering- Your guinea pig is angry or upset. This action is often a part of “strutting” with means aggression. They do want any attention and want to be left alone. If with another guinea pig, make sure to temporarily separate them to make sure they do not attack one another. If this happens when you are introducing them, try doing so in a different way.
Quiet Chattering- This can also be a sign of aggression but is not for certain. If the guinea pig is looking around making this sound they could be hungry or currently eating. If the chattering is quiet, your guinea pig could just be simply talking. My guinea pigs are very talkative and if I talk directly to them they make various noises including this. If looking at another animal, you directly, or another guinea pig while making this sound then look up at the “Loud Chattering” section.
Weeking/Squeaking- This common noise means happiness or excitement. When getting food or hay this is a common sound to hear. If your guinea pig does not do this please look at “Why is my guinea pig not talking”
Loud Purring- Loud purring is usually the sound of being annoyed. This could be towards other animals or humans. Personally I have noticed my pigs will make this sound if they do not want attention that day. Back when my cat was little the guinea pigs would make this sound towards him because he would sit on top of their cage.
Quiet Purring- A low and quiet purr often means that they are clam. To know the difference, the loud purring will be accommodated with the guinea pig trying to escape. This purr will include the guinea pig not wanting to move or try to itch the spot that you are getting at. My guinea pigs purr when petting the crown of their head in a loving way.