Haunted House?

I was sitting upstairs in my room doing my math homework. My mom was picking my sister up at school, and my dad was at work. I was the ONLY one home. Anyway, I was finishing up my work when this groaning/growling noise came from down the hallway. I thought it was the furnice or something, and although I was alittle nervous, I continued my work. Then I heard that noise again. It seemed a little louder this time, and I got really scared. It wasn't coming from the furnice, it was cming from my sisters room. I went down the hallway and was infront of my sisters door. It sounded like paper was being crunched. I started to open the door, and really loud growl came from the room. I was so scared that I ran downstairs with the phone, and covered myself with a blanket until my mom and sister got home. I was going to tell my mom, but I was afraid that she would htink I was crazy. So I left it alone. That night at dinner, my sister acussed me of going in her room (which she doesn't let ANYONE into) while she was gone. When I asked her why, she said there were pieces of computer paper thrown everywhere in her room. I told her I didn't go in there, and then I left it alone. I was totaly freaked out, and I still am. I've only told like, two of my friends.