Right, but that standard is more about the written standard language than about the language as spoken in Hannover. I know it's a trope that TV news announcers supposedly pronounce things like they are pronounced in Hannover, but that pronounciation is not a standard.
Says who? Not Wikipedia, which says that that's a regionalism and quotes sources. Where is the standard codified?
> What is the ending of the pronunciation of 'und' in your region? Is it 'd' or 't'?
This is a trick question: If I answer the same as you pronounce it, you'll say "see, it's standard!", and if I answer the other way, you'll say "well, it's not my fault that you don't speak Standard German™".
That said, it's 'd'. If anything, it's softened further and half swallowed to say something like "un'".
Why would there have to be a standard? My point is exactly that there isn't one that captures how actual people actually speak German. There is one for written German that everyone agrees on, but not for spoken German. And that's completely fine.
And coming back to the original Rat/Rad distinction, https://forvo.com/word/rat/#de and https://forvo.com/word/rad/#de do sound different. The second "Rad" speaker (from southern Germany) makes almost no 'd' or 't' sound at all, but the same speaker pronounces "Rat" with a very hard and clear 't'.
And for whatever it's worth, the Auslautverhärtung you referred to in several places in this thread is also just a Northern regional thing: https://de.wikipedia.org/wiki/Auslautverh%C3%A4rtung / https://en.wikipedia.org/wiki/Final-obstruent_devoicing#Germ...
Here (eastern Austria) "Rad" and "Rat" (can) sound different.