Do you use Alexa or any home automation. Could it be that the alarm is set there?

I haven’t tested if I set an alarm in the Alexa app and also in Sonos for the exact same time. Alexa alarms are chimes for me. 

If indeed they are Sonos alarms (and the above post is definitely a possibility), it means that at the time the alarm goes off, Sonos can’t reach the indicated station, for some reason. Rather than not playing at all, and missing the alarm, it defaults to a chime. 

You seem to have done the things I’d normally recommend, so I’d suggest that you submit a system diagnostic within 10 minutes of the alarm chiming, and call Sonos Support to discuss it.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

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

If you change the time by more than one minute, do you still have the issue? I’m speculating that the music site might go down (for a few minutes) for maintenance at 9:00. Another possibility is that 9:00 is a favorite time for the station. Stations contract for a certain number of simultaneous streams. When the limit is reached the station may dump users with long time connections or block new connections.

I don’t use any home automation other than Sonos

Thanks!   I will try that

I will try changing the time...Thanks!