At the start of races Lakitu 'when races are starting': Ready? Racers: Oh yeah! Ready as a racer! Activate the Kart! Let's-a-do it! Here we go! Ready, Lakitu: Alright then! Get in your positions! Set your marks! 3, 2, 1, START!
Unless you have a Mario Card (and you can turn the option off from there), all non-Mario Card users will have to live with the annoying announcer, I'm afraid. :(