I had two PLAYBARs for years, and never experienced this. Are you sure it’s not something the TV is sending to the PLAYBAR via the optical cable, and the PLAYBAR is just reproducing what it is sent?
Can this sound be reproduced? If it can, I would recommend that you submit a system diagnostic within 10 minutes of experiencing that sound, and call Sonos Support to discuss it. They should be able to tell if it’s an issue inside the PLAYBAR, or if it is being sent by the TV across the optical connection.
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 phone folks, there are more options available beyond just the diagnostic analysis.