I have absolutely zero ability to take your descriptions and convert them into an understanding of what you're trying to convey. Like what could this possibly mean???
> ...which is like a mouth full of down feather.
> ...which is like a mouth full of down feather.
This means speaking soft, muffled words - roughly the way you'd sound if you had your mouth full of something soft. Like feather. Or food.
Not a perfect analogy, but hey, works as a hash for an accent, at least among the people I know locally.