Though your case seems different, but these beeps can be turned on/off through Toyota techstream or apps like Carista, using the OBD port. I have disabled the seat belt beep in two of my cars, on both Toyota Aqua and Corolla. There are options to set some other stuff as well, like the sensitivity of auto-headlights, the short or long press to open boot etc. It is often mentioned in the customizable features heading in the owners' manual.
But as I said, your case seems different.