Popcorning- usually means they are happy or it could also be to show an overflow of emotion
Rumble Strutting - a dance like movement when a male piggy is romancing another guinea pig. A female can also make this sound if she is in season. A rumble sounds deeper than a purr with a vibrating effect. While making this sound a guinea pig will sway their hips and walk around another guinea pig. This is known as the mating dance.
Mating - When a male guinea pig is ready to mate, he will lower his head and walk towards the female. His steps will be deliberate to indication his intentions. They make a distinct rumbling sound as part of their mating ritual. He will even wag his bottom side-to-side a few times. Some males go as far as to do a mating dance of sorts where they put their front legs up on surrounding objects to attract the female’s attention. This move might also include some sort of waving or wiggling.
The female will show interest by squeaking, she’ll squeak louder the closer the male gets to her. If she is by chance uninterested, because she isn’t in heat or at least not at the right part of her cycle, she will instead snap and bite at the male or run away. If the male continues to persist she might even urinate in his face to send a clear message.
If the male is not aroused and the female is ready to mate she will sometimes walk toward the male using the same steps and stance he would use to approach her. Sometimes a female will even back up against the male to encourage him to mount her. This is perfectly normal, don’t worry about any of their actions and just let nature take its course. The guinea pigs will know what to do.*From http://www.guineapigstips.com/
Chirping - it's rare to hear a guinea pig chirping. It usually means he's either very upset or very happy.
