use PWM buzzer on notification module. To activate set moduleConfig.external_notification.output equal to the PIN_BUZZER. If another value is set, the traditional digital mode is used

src/modules/ExternalNotificationModule.h

@@ -12,6 +12,8 @@
  */
 class ExternalNotificationModule : public SinglePortModule, private concurrency::OSThread
 {
+  uint32_t output = EXT_NOTIFY_OUT;
+  
   public:
     ExternalNotificationModule();