Problems with recording

Recently i have purchased a Macbook for my brother. He uses the macbook to record his mixes. The problem were facing is after were done recording and we burn the track onto the cd. When we listen to the tracks that he made there are some parts of the tracks where static would come out. . .and some parts that were clear. Could it be that our volume is to high and its causing static to come out? or could it be something else? Could someone please help me?