I'm hoping this helps someone else. I saw multiple threads of people struggling to resolve annoying random two tone notification sounds on their Samsung TVs.
In my case, even after disabling SmartThings and turning off notification sounds, it still occurred.
It ended up being an Amazon notification. I cleared and deleted all notifications via one of my Alexa devices (I had one purchase reminder notification.) This resolved the issue. You can say "Alexa, play notifications" then "Alexa, delete notifications".