The word 'Noise' in communication theory is a barrier to communication that may weaken or destroy a message that is trying to be relayed There are a number of ways to classify noise. It can be subdivided according to type, source, effect, or relation to the receiver, depending on circumstances. In order to make the classification more compact, noise sources can be divided into two main groups: • Noise whose sources are external to the receiver (External Noise) and • Noise source created within the receiver itself (Internal Noise). types include: Shot noise; Johnson noise; Partition noise and White noise