Is your SatNav an Alpine branded unit, as if so then it will be the same unit as in my 2014 25AE.
Unfortunately, I don’t know how to switch off the warning, but I find that the SatNav map is a little out on its location, not by much but enough for it to think that you are still in a 30 when you have passed a 50 sign say. It is a little annoying when you know you are not speeding, but is always a good safety check when you are on unfamiliar roads.