FMS4 audio streaming - low volume causes sound distortion

I have an application that is broadcasting live audio and clients are subscribed to the channel and receiving live audio stream.   Subscribed clients have audio volume control in Flash application that can change the volume level.  When the volumne is low or muted it causes erratic distortion. For mute, I set it to pause the stream which fixes it but for low volume I'm not sure how to fix this so the sound is clear without any distortion.

Thanks

Chris