Sound balance drifts

Thanks for stopping by the Apple Support Communities, drumblestein,

To help further isolate and troubleshoot the issue you've been experiencing with the audio balance on your Mac, we would recommend going through the steps below:

1. You mentioned noticing this seems to been reproducible, occurring when you make a change such as which output device is being used or you adjust the volume. To isolate the issue between the system as a whole, we would suggest creating a new user account and making these adjustments there to see if the issue persists: Set up users, guests, and groups on Mac - Apple Support. If it does not occur in the new user account, the issue is likely to be with settings or content within your existing user account. If it does, we can move onto further troubleshooting with the next steps.
2. Start your computer in safe mode: How to use safe mode on your Mac - Apple Support. The main reason for doing this is because during the boot process, safe mode scans your startup disc, and will make repairs to identified issues along the way, where it can. Because of this, booting into safe mode can often resolve issues.
3. If you have not already, see if the issue occurs regardless of the app you're using for audio playback.

Don't hesitate to respond back if the issue continues after that.

Best!