I have two guinea pigs, they're pretty neat. I was driven to buy them because they were cute, but I knew I would have to give them food, affection, and exercise.

Exercise. Guinea pigs need daily exercise and if you try chasing them around in a big room you'll find that they're quite fast, despite their stubby legs. I let mine run around in my Dining room, and they are very interesting to watch. I've heard them whistle, squeak, purr and chatter and I'm beginning to decode what some of these sounds mean.

Whistling/siren sound-They make this when they're trying to relocate each other, or when they want their owner. (This isn't really a whistle, it's just so high pitched it sounds that way).
Loud squeaking and chattering-This means they're mad or in pain.

Purring-This means they're happy and enjoying themselves.

I wish I could find out more, and maybe even duplicate these sounds. But for now, all I can do is watch these amazing animals at work.