Be not a feared ; the isle is full of noises - explain!

These remarkable and conspicuous lines have been derived from the romantic comedy, The Tempest written by William Shakespeare. Here Caliban tells Stephano and Trinculo not to feel afraid of the sounds that they may hear from unknown sources on this island. He describes the charms and delights of the island. This speech expresses the poetic nature of the monster Caliban. 

The island where Prospero lives is full of sweet sounds, voices and sweet melodies. These sweet sounds and voices are a source of pleasure but they do not have any harmful effect on the characters. Obviously, this island is a strange and mysterious place. Prospero sends Ariel, an airy spirit to hear the secret plan of Caliban, Stephano and Trinculo. The three are in a drunken state. Suddenly, Stephano and Trinculo sing a couple of lines. They feel surprised when somebody, invisible to them, plays the tune on a tabor and pipe. Caliban tells them that there is nothing to be afraid of this invisible music. He is completely known to the supernatural music of the island. He has heard the twanging sounds of thousands of musical instruments humming in his ears. He has also heard voices sometimes which lured him to sleep due to their melodious sounds. So he assures them that this island is full of different sweet sounds. 

These different sounds are amusing to them but not harmful. Indeed, Shakespeare's poetic and fine observation about things around him is obvious in these lines.