Guinea pigs frequently squeal when they're scared. If you hear your guinea pig persistently squeaking, it could mean that a loud sound from outside bothered him and he's alerting your other cavies to the approaching peril. read more
Whining: A whining or moaning type of squeak can communicate annoyance or dislike for something you or another guinea pig is doing. Chirping: This sounds just like a bird chirping and is perhaps the least understood (or heard) noise that guinea pigs make. read more