Hi @Ibsearcher, welcome to the Sonos Community!

I’ve not heard of this specific noise before, so I would recommend waiting for the issue to occur again and submit a diagnostics. Once you’ve submitted the diagnostics, take note of the confirmation number and reach out to our support team for further troubleshooting. They may want a video of the issue, If you can also record one it will help with figuring out what the sound could be caused by.

I hope this helps!