Re: When does 't' pronounce 'd' in AmE accent?
When the t is between vowel sounds it's often pronounced as a d.
Metal and medal sound the same unless the person is really enunciating. As a child, I though "congradulations" was the spelling because that's how it sounds.
Some regions do it more. Some less. In Philadelphia, they drink "wudder" and after 10 years here, it still sounds strange to me.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.