Ed - Hey, thanks for the clarification. You're right that what I was hearing is actually called a "yod," which is a term I was previously unfamilar with.
However, in my defence, according to Diction for Singers (the text I was taught out of freshman year) a glide is "characterized by a movement of the articulators from from one position to another. The glides in English are [r], the y sound [j], and [w]." Therefore, when I heard the 'y' sound added to the word "knew," I assumed that it was just an innapropriate insertion of the [j] glide. I wasn't aware that there was a term more specific to the dialect and context. Thanks for setting me straight on that.
PS: Suzie, I think MC and Ed pretty much covered it. Please let me know if you'd like me to try and clarify anything else. I hope the review was otherwise helpful for you. Best of luck with your future endeavors.