In case anyone else is banging their head wondering why there is no audio on their mobile device, it looks like there was some change/glitch in the audio handling of the AMP player. This is on an Android 7.0, so not sure if it affects other versions or Apple devices.
I clicked the link in the email today for #556 Video Podcast: The Implications Of Non-Shotgun Shotguns and Brace Equipped AR pistols. It launched as normal but there was no audio and no way to turn it up. I then changed from the mobile based browser by clicking 'Request desktop site' and it re-launched, but this time there was the small slider to control the volume, but it is now defaulted to the off position.
Later I confirmed the same on a Windows/IE system, the link now launches the player with the audio slider defaulted to OFF.
SA