I'm not sure, maybe shes calling out to other piggies? If the noise is like a "wheek" its wheeking, my guinea pigs do it when they want treats and hear me opening the fridge. You should really think about getting you guinea pig a friend. It will make your guinea pig thrive and even with plenty of human attention it doesn't fill up the need to have your own species to run and play with. Is there a specific reason why your piggy doesnt have a friend? One more piggy doesnt take up much space...