Try these steps in order:
- Select the correct output device.
- Go to Start > Settings > System > Sound.
- Under Output, choose the headphones or Bluetooth audio device.
- Make sure the volume is not muted and the slider is turned up.
- Set the playback device as default.
- In Start > Settings > System > Sound, select Sound Control Panel under related settings.
- On the Playback tab, select the headphones or Bluetooth device, then select Set Default.
- If using a communications app, set it separately with Set Default Communication Device.
- Check accessory connections.
- For wired headphones, make sure the cable is fully inserted.
- If the connection is secure and audio still does not switch, disconnect and reconnect the cable.
- If using a 3.5 mm audio device and it is not detected right away, disconnect the Surface Connect cable, then reconnect it to re-detect audio devices.
- Close audio apps, then remove and reconnect the accessory.
- For Bluetooth headphones, confirm pairing.
- Make sure the Bluetooth headphones are paired correctly.
- If Bluetooth audio keeps switching or does not stay connected, use the Bluetooth troubleshooting guidance here: Fix Bluetooth problems in Windows.
- Turn off audio enhancements.
- Go to Start > Settings > System > Sound.
- Select the playback device, then Properties.
- Open the Enhancements tab and select Disable all enhancements, then OK.
- If there is no Enhancements tab, select Advanced and turn off any available audio effects.
- Run the automated audio troubleshooter.
- On Surface, run the audio troubleshooter in the Get Help app.
- It automatically runs diagnostics and attempts to fix most sound and audio issues.
- Check simple hardware causes.
- Make sure headphone or speaker power is on if required.
- Check for loose cords or cables.
- If using USB audio, try a different USB port.
- Unplug any headphones temporarily to test whether Windows is holding audio on another device.
If the issue is that audio switches by itself, the most likely causes covered here are the wrong output device being selected, the device not being set as default, Bluetooth pairing problems, or audio enhancements interfering.