Little Pippin makes a purring noise at lap time when my daughter is stroking her back.. I've read this means they are not happy but have also read it means they are happy .. ?
I've often wondered that as I've heard conflicting answers also! But my little Cinnamon purrs when you pet her and especially if she's out for her TV time which she loves lol and that's usually when she will stick out her back legs and totally relax so I assume it's a happy sound!From what I've told it is enjoyment. Whenever I hold my piggies and rub them they usually pur.
Check this website out, it has a list of guinea pig noises with a sound file
http://jackiesguineapiggies.com/guineapigsounds.html