Google made a code change recently and it caused ALL YouTube video paged to ope with the audio "muted". This ISN'T a problem with FLash Player, nor can it be fixed by Adobe. It IS a problem with Google's website cocde for YouTube.
The solution is to manually adjust the volume, until Googlre fixes the code. The following video shows how to do this.
Hover over the "speaker icon" and the "volume slider" will appear to the right. Slide it to the desired level. You may or may not have to repeat this for every video you watch.
AdChoices