I found this:
* Please note: Embedded in an alert message is the amount of time for which the alert is active.
The WR300 will continue to display the alert until the expiration time. Ex: END 12-55P indicates
the event ends at 12:55 PM.
In the WR300 Owner's Manual.
This might imply that the radio shuts off the audio based on the alert expiration. I am not sure if this refers to something on the display or would also include the radio sound being active. It would be interesting if someone could observe this.
Do you hear the three FSK (modem-like sounds) tones at the end of the message. My Wx radios (Reecom and MTS) mute the audio after the first "squawk".
My APRS TNC requires a good S/N ratio signal before it will decode. Since S.A.M.E. is pretty straightforward, weak signals might cause problems. It does sound like there is no problem activating on the alert, though from the descriptions. So this might not be the case.
Greg H.