If the audio input is NOT connected to the source when the noise occurs: There may be signals from the environment which might be picked up by the speaker and therefore produce the noise. * Connect the audio input to an MP3 player or a computer If the audio input is ALREADY connected to the source when the noise occurs: There may be dust or oxidized metal on the connection. * Disconnect the connections, clean the connecting parts with a soft dry cloth and then reconnect them There may be dust or oxidized metal on the volume control parts inside the speaker. * Slowly adjust the volume control knob backward and forward