What do you mean by ‘kicks in’, and what model of speaker is doing this?

It sounds like you have Autoplay enabled. 

It plays a recent track that I have selected from my music library. It plays it on my Beam and two linked Play 1s. What made it really spooky the first time is that it played a tune that I was actually playing on my button accordion. Admittedly I had listened to that tune earlier, as I was learning to play it. My Sonos system definitely responded to my playing. 

Thanks nic9669a, but how do I disable Autoplay? I can't find that option. 

Autoplay would only be a factor if something was connect to the line in source of a Port, Five, or Amp...or if audio was playing from the TV.

I’m thinking squeezebox is connect to your Sonos room and the command to resume playback is coming from there.  I would go through the squeezebox settings, or logs if that exists for squeezebox.  If that doesn’t help, I would run a diagnostic right after the issue occurs, then contact Sonos with the diagnostic number.  They should be able to tell you were the playback command came from.

Many thanks Danny.

Squeezebox is not an application or electronic instrument. It is just my colloquial name for what is a large sort of concertina, a musical instrument that works by air being passed across reeds - like a mouth organ. So my Sonos is reacting purely to a sound. 

Of course my Sonos system does provide audio for my TV and it is the same units - beam + two play 1s - that Sonos uses when it unexpectedly starts up. The TV can be voice controlled but requires a button to be pressed on the handset when operated this way. 

Alan 

Ah. I thought you were referring to this.  https://mysqueezebox.com

You still could do the diagnostic to help figure out where the play command is coming from.

I ll do that. Thanks Danny. 

Alan