For a presentation to reach its objective, several things must happen. Noise is anything that interferes with the accurate transfer of the message and it can occur at any point in the communication process. Physical noise could be a phone line with static, constant interruptions or handwriting that is difficult to read. Psychological noise could include not liking the speaker, being preoccupied with other thoughts or already having one's mind made up on an issue. Semantic noise refers to misunderstandings caused by the choice of words, so it is important to avoid jargon and technical language unless your audience shares the same language.
Perceptual noise relates to the values, attitudes and backgrounds of the sender and the receiver.
If you think you can or you think you can't, you are right. All sorts of irrational fears take over. It is important to realise how unreasonable these fears are. You may possibly set your own limitations by telling yourself that you cannot achieve a particular goal. This type of attitude applies as much to presenting as to any other task.