Removing noise wheh mic attached to Stream on Media server

I am using these settings for media server but there's too much noise when a mic is attached to stream. Code is as following, can you suggest changes to remove the noise for more crystal clear voice?

public function initMicrophone():void
{
    mic = getMicrophone();

    if (mic == null)
    {
        trace("No available microphone");
    }
    else
    {
        mic.setLoopBack(false);
        mic.setSilenceLevel(10, 20000);
        mic.gain = 60;
        mic.addEventListener(ActivityEvent.ACTIVITY, micActivityHandler);
        mic.addEventListener(StatusEvent.STATUS, micStatusHandler);

        mic.codec = SoundCodec.PCMU;

    //mic.codec = "Speex";
    //mic.encodeQuality = 10;
    //mic.framesPerPacket = 2;

    }
}

private function getMicrophone():Microphone
{
    var mic:Microphone = Microphone.getEnhancedMicrophone();
    var options:MicrophoneEnhancedOptions = new MicrophoneEnhancedOptions();
    options.mode = MicrophoneEnhancedMode.FULL_DUPLEX;
    options.nonLinearProcessing = true;
    mic.enhancedOptions = options;

    return mic;
}