Increase the volume at the source device (ie, the MP3 player, or the mobile device).
If the audio signal from the source is too low, the speaker would detect this low signal as noise and mute the noise. Therefore, the music from the speaker would be intermittent if part of the music has a low audio signal. Similarly, if the audio signal of the whole piece of music is low, there would be no music from the speaker at all. This can be solved by increasing the audio signal (ie, volume) from the source device.