wsmaster,
It sounds to me like a problem with the G.711 implementation. I’ve seen such behavior before… some work, some don’t. Try adjusting the audio settings if possible.
You can post the output of ffprobe, and/or describe your stream and device/model in detail so we can identify if a certain implementation exhibits this behavior. Is it a-law or mu-law? G.711.0 or G.711.1? Sample rate and bitrate?
Alternatively, you can transcode the audio portion before the stream gets to Wowza. Some examples here: Frequently requested FFMPEG command examples for Wowza