Why might she do this?

I have a 2 year old niece. Recently my sister (her mom) and I were talking about the little things she does. My sister has become concerned. She will flick her hands. She also covers her ears alot. My sister at first thought with the covering of the ears she might have an ear infection, but no fever, and even a quick trip to the doctor proves other wise. She has been doing this for a couple months now and I my sister started to look up these behaviors, since she has never seen this before in children. My niece talks perfectly fine for a 2 year old. She can say her ABC's without much help. She can count to ten almost, sometimes she gets a couple numbers mixed up she is only 2. She is very social and loves to be around people and other kids. I think it's probably just a tick she has. She does not fit any other warning sign for autism except the hand movements. But are there any other things that might be causing her to do this?