How can I clear buffer in XAudioJS

I am using XAudioJS (http://ift.tt/1RgILaf) for a current project and I need to do the following:

• On mousedown, a sine wave should be played. I did this by generating a sine wave in the background and when the event is fired, the volume is set to 1 or 0 accordingly

• When a user clicks on a div, a sequence of samples is being played. Other userinput is paused during this time

I could manage to do both independently but I can't bring them both together. When the user clicks on the div, the audio sequence is played but first a bit of the sine wave which was muted was also played

I suspect that it has to do with the buffer of XAudioJS. It is not cleared and therefore plays parts of the sine wave which is still in the buffer. I can't figure out a way though, how to clear it before playing the sequence.

Also I think I don't really understand what buffer-low and buffer-high for XAudioJS exactly means or which values are better for performance and which are not.

Here is my underRunCallback function I gave to XAudioJS:

var sample = []; // samples for the sample sequence
var samplePos = 0; // counter for samples
var sampleRateUsed = 8000;
var frequencyUsed = 550;    //frequency for sine wave
var frequencyCounter = 0;
var counterIncrementAmount = Math.PI * 2 * frequencyUsed / sampleRateUsed;

function underRunCallback(samplesToGenerate) {
    //Generate audio on the fly=>
    if (samplesToGenerate == 0) {
        return [];
    }

    var tempBuffer = []; // buffer that is returned

    // create sine wave on the fly:
    if(!isPlaying){
        while (samplesToGenerate--) {
            tempBuffer.push(Math.sin(frequencyCounter));
            frequencyCounter += counterIncrementAmount;
        }
        return tempBuffer;
    }

    // NEED TO CLEAR BUFFER HERE

    // play sequence of samples:
    samplesToGenerate = Math.min(samplesToGenerate, sample.length - samplePos);

    if(samplePos == sample.length){ // if all samples of sequence played
        input_paused = false; // allow new userinput
        isPlaying = false;
        xaudioHandle.changeVolume(0); // mute audio
    }

    if (samplesToGenerate > 0) { // if new slice of samples is needed
        tempBuffer = sample.slice(samplePos, samplePos + samplesToGenerate);
        samplePos += samplesToGenerate;

        return tempBuffer;
    } else {
        isPlayingB = false;
        return [];
    }
}