Try something along the lines of:

Mac OS > System Preferences > Notifications.

Scroll down to Sonos and click on "None".

Thanks. Checked and that setting was already off. Tried turning it on, then back off. Same behavior.

Thanks for the attempt. 

Hi @J. Auer, welcome to the Sonos Community!

This is a very strange one, I’ve personally not seen this happen before and I’m not sure what would be causing it.

Since the issue seems very easily to replicate, I’d recommend reaching out to our support team as they have the tools available to troubleshoot and resolve this issue with you.

I hope this helps!

Thanks. I’ll reach out to support.