I guess I needed to charge the battery full as it cleared up afterwards. This tells me the 130W PSU may be somewhat below actual requirements.

For troubleshooting of this problem you can just follow these steps-

Update Audio Drivers:
Go to Dell's support website and download the latest audio drivers for your XPS 15 9570.   
Uninstall the current audio driver using a reliable uninstaller like Display Driver Uninstaller (DDU) in safe mode before installing the new one.
Check Audio Settings:
Ensure correct output device is selected.
Adjust volume levels and playback settings.
Disable any audio enhancements or equalizers.
Disable Audio Enhancements:
Try disabling any audio enhancements or equalizers in the sound settings.
Run Audio Troubleshooter:
Windows has a built-in audio troubleshooter. Try running it to identify and fix common issues.   
Check for Conflicts:
Temporarily disable any audio-related software or applications to see if they're causing conflicts.
Test with Headphones:
Try using headphones to isolate the issue. If the problem persists with headphones, it's likely a software issue. If the issue is resolved, it might be a hardware problem with the speakers.
Check for Physical Damage:
Carefully inspect the audio jack for any visible damage or debris.

@anyabaker​ 

I am wondering if my cheap Bluetooth headphones are borked. I am awaiting on a new AX210 Wi-Fi card which is dramatically more sophisticated. The AX210 fits the slot fine but the BE200 is slotted differently and I have not seen a BE200 that is slotted the same as the AX210.

This should fix some issues. I hope. The card is close at hand so maybe next weekend I have that installed.