Help with A57 volume control

We know that the printed manual that came with the camera is worthless. I don't have sound when I play back videos I've shot. In the video menu Audio Recording is set to "on".

In playback menu 2 Volume Settings set at 0, and is grayed out. I've tried every mode, etc and it stays grayed out. Obviously I'm missing something, Can anyone tell me what I have to do to enter the volume setting to adjust it accordingly? Thanks in advance for your help.