Disconnecting Spotify won't necessarily help, although that may depend what you mean by that.

Have you played another source on any affected speakers?

Do you have any alarms set in the Sonos app? Do you live in an apartment where you have neighbors that could possibly connect to your Sonos speakers over AirPlay? Does anyone else have access to your Spotify account?

You might try logging in to your Spotify account on a web browser and using the “Sign out everywhere” feature. Or go to the “Devices menu” in the Spotify app, and any device that you don’t recognize, tap the “...” and select Forget device.

Did someone use Spotify Connect on your system? Because the connection to their phone stays live even when they leave your home. And when they play Spotify they do not hear anything, which makes them turn up the/your volume…