Why are some people so .................?

annoying? Some people talk on top of their lungs, when people are around, all they talk is rubbish. I am tired of my sister talking on top of her voice, when I am in another room. We share the apartment, it's 2 bedroom, and a living room and kitchen. She will sit in the living room and talk of top of her voice. It's disturbing and the things she says don't make sense at all. It's 24 hrs when she is at home, and most of the 24 hrs she is at home. She is always talking on the phone or online chatting on the phone. Its annoying especially when there is another person in the house. Its really disturbing. Why are some people like this?