I know this is an old thread, replying on the off chance that someone else runs across this.
I'm the developer that added this notification and can give you some background as to why it was added and when and why you'll see it.
There are some monitors which report support for audio, but due to lacking speakers they can't actually play audio. Sometimes it's because there are no speakers plugged into the speaker jack on the monitor, and sometimes the monitor doesn't have a jack to plug speakers in to. When audio is played to one of these monitors, you won't hear anything.
For every audio endpoint in the system, Windows calculates a weighting value for how preferred it is to be the default audio endpoint. When an audio endpoint comes in or goes away, those weighting values are compared and the highest weighted endpoint becomes the default. When someone manually selects an audio endpoint, it overrides that weighting value, manually selected endpoints will always become the default if they're available.
When a monitor has never been manually selected to be default and becomes the default for the very first time based on the weighting rules, we pop up the above notification so you will be aware that audio is now going to that monitor in case it doesn't have speakers. This notification will only ever pop up a single time for a monitor, regardless of action taken to dismiss it. We want to make people aware of the audio endpoint change due to the potential issues with using a monitor for audio, but we also do not want to annoy people with useless or excessive notifications.
If you have multiple monitors in the computer, you should see at most 1 notification per monitor. If you're seeing this notification more than 1 time per monitor, then that points to an issue where the audio endpoint settings data is being lost for the monitor.
Lost audio endpoint settings data will result in customized audio endpoint names being lost, format and effects preferences being lost, and causes issues with default audio endpoint selection in general because manual selection preferences are stored with the endpoint settings.
Audio endpoint settings are retained across OS and driver updates, but audio endpoint settings would be lost if the driver were uninstalled and reinstalled, or if the audio driver for the monitor were activating a different PNP interface, making it appear as though it's a different monitor.
Gary Daniels
Principal SDE, Microsoft Windows Audio
