Apple Watch S4 dinging

Settings -> Notifications -> Messages -> Repeat Alerts. Set to Never.

Just guessing. If you setup a new phone recently the default isn't Never.

 

Sounds like the breathe app. But if it is then it should show on your screen.

 

Is it the "Time to Stand" notifications, where it lets you know if you haven't stood within the first 50 minutes of the hour? Not the initial one at the 50 min mark, but the one for completing it... aka... If you get the 50 min. mark notification and then complete it in the last ten minutes of the hour, it gives a little chime to let you know you completed the stand for that hour. (Though that's a double beep I think).

Also could someone be trying to walkie-talkie with you?

 

I am getting this with the carrot weather complication. If you are using carrot, open the app itself and see if it makes the same ding when the app updates. It is annoying because it always makes me think I have a new notification. I haven’t seen a way to turn it off other than removing the complication.