When you hear guinea pigs squeaking or whistling, what you are hearing is the natural way for guinea pigs to communicate.
Amongst guinea pig owners, the term used is ‘wheaking’.
They will wheak to both other guinea pigs and humans as a way of communicating what they want or even as an expression of excitement.
Once they get to know you, you will often hear them wheaking, demanding your attention for food.
You may also notice them communicating like this to each other if you have guinea pigs together. Often they will communicate like this when it comes to matters of food or when playing or squabbling over something.
In the wild, they may use it to seek one another out or find a herd.
It is nothing to be wary of, and if they are wheaking at you, it is a sign of familiarity.
My guinea pigs know the sound of my footsteps and even before I have come into sight, they know I am coming and they start wheaking away and I know they are wanting to be fed.
This proves them to be quite intelligent and intuitive animals.
But as a guinea pig owner it is one of the most delightful sounds you could hear.