What is this funny sound?

Question
My guinea pig makes a funny little noise when I am holding her on my lap and pet her head. Is this because she doesn't like it, or is she saying she does?  It's just a quick little purring sound. Do all guinea pigs make this sound?

Answer
That little purring noise you are referring to is telling you she likes that. Guinea pigs don't purr like cats, but they do make a short little sound that is very much like a purr.  She's telling you she is enjoying the attention.  It's her way of saying 'thank you.'