I've seen this happen more than a dozen times where I try to use the Touchpad from a standby state and there is no audio. If I restart the device it comes back no problem every time. Not satisfied with this I came across the issue elsewhere and was pointed in the direction of using a app to restart the audio when noticed it's not working. Install preware first (New Touchpad? Here's your "Get Started" guide - PreCentral Forums) then search for an app called "PulseAudio Restarter". I haven't had to use it yet but the app only takes 5 secs to run. Might be of help to others who notice no sound and don't want to reboot.