My rat is making worry some sounds. Please help.?

My rat is making some very strange sounds, she was making them a lot this morning too. She won't stop making them, they sound like a congested squeek. I'm not sure if she is just being very vocal, or if this is normal, I got her 3 weeks ago from a pet store, and I take them out a lot and they seemed to be very healthy. But I'm worried something may be wrong with her, I also got one of her sisters from the same litter and there seems to be nothing wrong with her. I am a first time rat owner and terrified she may be ill. Does anyone know what may be wrong?