Guinea Pigs have several different noises that they use for communication; first, there is the high-pitched "Wheep!" noise. This one is used when excited (usually about food), or, ocassionally, when hurt or distressed. There is a separate noise for when they are unhappy, but because I rarely heard the noise (I was not the type to torture my guinea pigs in the name of empirical discovery) I was unable to distinguish the sounds.
The second noise that the Guinea Pig will make is the "chut-chut" noise. They do this when they are exploring or running around.)
Finally, somewhat related to the "chut-chut" noise is the "brrrtt" noise. This is primarily a noise used for domination (social as well as sexual) and as a supplement to the "chut chut" noise.