I believe I know what is causing the sound not to work. Apparently there was a change in how the raspbian OS handles sound. See
https://www.raspberrypi.org/blog/new-raspberry-pi-os-release-december-2020/ for some more details. But, in summary the Dec 2020 raspbian release changed the sound server from ALSA to PulseAudio. I understand there are some good reason for them doing that but it seems to have broken audio from AM for some reason.
In my case I decided to download a raspbian lite image from
https://downloads.raspberrypi.org/raspbian_lite/images/. I specifically took the 2/14/2020 release which still uses the ALSA sound server. This image works perfectly for me. I will note though that you can't upgrade the OS as it will install the PulseAudio sound system which will likely break AM sound again.
In my research I ran across an article somewhere that said you could remove the pulseaudio packages and everything woud default back to alsa. Another option was to add some parameters to the /boot/cmdline.txt file to re-enable alsa compatability too. I didn't try either of these options though so I don't know if they will work or not.