Question about US English

Recently, I've noticed in conversations and in media that many Americans are pronouncing the contracted negation "n't" as a a reiterated d+short-i+nt instead of schwa+nt. Has anyone else noticed this? Is there a local dialect origin for this or is it novel? It has a subtle effect on the rhythm of the word, which might have repercussions for text setting (compare diduhnt with did-dint).