What audio source starts playing and have you considered maybe also changing your WiFi password too, just in case?

Strange it has happened many times at 3am aswell?

The 3AM makes me think of cable boxes and TV’s that are activating their systems in order to do download checks for new software…..

Which, of course, would be belied by the whole “confirmed no devices are connected” aspect, so I guess my fallback would then be Spotify Connect from someone outside the home, since that can’t be “seen” by looking at Sonos. 

It would be extraordinarily helpful if you were to submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it. The 10 minute thing is to ensure that the “activation” even is captured in the log file, which has size limits, unfortunately. It’s possible that if you don’t use the Sonos at all until such time as you run the diagnostic, it might be there still, but I’m unsure of exactly what data gets stored, and how frequently or how it gets flushed out. Could be time based, could be activity (size) based?

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution, inasmuch as it should show what device/system started the playback. 

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your Sonos system and network.

Thank you all. The music is from my spotify account. I think the amp may have gotten wet during a storm and its truly a bug. I will definitely try the diagnostic approach.