I vaguely remember some similar reports awhile ago.
I hope someone with a better memory or has experienced the issue. Can provide more added information and assistance.
As my search of the older messages didn't find the information I was looking for.
Same here. And the worse part is.... I can't recall either the cause or the solution.
But.............If the problem occurred here... with my setup.
My first thought would be what changed on or about the day/time of the first "buzz". Was there something new added to the powerline? Christmas lights? A gift?
I'd then check my activity log.... was there anything happening at the time of the buzz. Timer, sensor, macro?
I don't know of anyway to "cause" the chime to buzz.... so I can't look for that. I might try switching the code (like from A to B) on one to see if that stops the activity on it. If it does... that might lead in the direction of a solution.