Volume slider movement causes audible clicking

Happy New Year All!,

    Trying to finish up this real simple player app.... play two mp3's at the same time and has two volume sliders to adjust each track.

When changing the volume you can hear audible clicking, almost like clipping but it happens in both directions. I have a slider_mc that is bound to a rectangle the

length of the slider. I divide the .x position against the total length to get the volume adjustment and send that to the sound channel, pretty standard I believe.

function adjustVolume(myEvent: Event): void {

     mainVolume = control_mc.slider_mc.vSlider_mc.x / mySliderLength;

     trace(mainVolume);

     framesA = Math.round(control_mc.slider_mc.vSlider_mc.x / mySliderLength * 200 + 2)

     control_mc.slider_mc.groove_mc.gotoAndStop(framesA);

     var myTransform: SoundTransform = new SoundTransform(mainVolume);

     if (mainChannel != null) {

         mainChannel.soundTransform = myTransform; 

     }

}

Anyone come across this of have a suggestion?

Thanks

Craig