The Apple TV plays two audio sounds from two different sources at once!

Force-quit the apps that you think are bringing these audio streams, from the App Switcher.

Then try again.

If it happens for multiple streams within one app, then do as for any misbehaving app:

1. Force-quit the app, then relaunch and try again.
2. If the issue persists, force-quit the app, restart the device, then relaunch and try again.
3. If the issue still persists, delete the app, re-download and try again.
4. If the issue still persists, then contact the app developer for further assistance.