Win 8.1 Sound mutes and unmutes randomly

Over the past week or so I have experienced a problem with the audio on my HP Envy Touchsmart 15-j002ax Notebook

Randomly, my sound will mute/unmute itself, sometimes many times in a row. I'm using the built in Radeon HD Audio with the newest HP drivers (according to the HP Support website)

When the speakers mute or unmute an icon appears automatically in the top let hand side of the the screen and it displays the percentage of volume, the same as the speakers icon in the system tray. However the percentage is displayed in a black box icon and is not the normal speaker icon. The f6 key on my keyboard illuminates when the random mute occurs and disappears when the random unmute occurs. Depressing the f6 key when a mute occurs does nothing. However pressing the volume adjustment keys f7 or f8 unmutes the speakers. Also if I display the system tray speaker icon and click the mute symbol the sound is unmuted

However, the random muting and unmuting keeps occurring and I cannot control it or any length of time