Clicking noise of ofxOpenALSoundPlayer and ofSoundPlayer

When you continually play the same sound by the setting of “setMultiPlay(false)” on soundPlayerExample of version iPhone 007, I notice there is a clicking noise.
It occurs except at version 4.3 of iOS.
It is the same for ofxOpenALSoundPlayer.
Does anyone know how to solve this problem? Please advise me of the solution.