Why is my guinea pig extremely vocal?

Please help me lool I rescued a guinea pig from a rescue who was very underweight and ill.. and he would just sit in the corner so depressed. So I got him a friend, a baby guinea pig from a rescue and he has perked up so much and so happy now. But the thing is he is SOOOO vocal. Every time i come up the stairs he whistles.. and he is in my room lol when I come in he runs straight to me and whistles. When I am in my room on my computer and just move a little bit he whistles! He is such a cute old boy but is there anyway of stopping him from whistling so much? I give him lots of fresh hay and veg but that only stops him from whistling for a while. He is in a MASSIVE indoor cage. What do you think is causing this obsessive whistling? Maybe that's why his other owner gave him up? But of course I will never ever give up this sweet boy.. he will be with me forever <3