Woman-speak: The Word "You"

My brother the music executive sent me some pop CDs that I asked him for, and sent along the Kelly Clarkson greatest hits album -- which brings me, in a roundabout way, to something I've idly thought about off and on for some time.

It's the pronunciation of the word "you" with a short-e sort of inserted: yeah-oo.

Clarkson uses it in the chorus of "Since U Been Gone", not during the title phrase, but when it's the stressed syllable in the line:

Thanks to YOU
Now I get
What I want...
Since U been gone.

It's not unique to Clarkson, nor, AFAIK, to the changed vowel sounds (ar for er, ah for I, eh or long-a for ee, to name some) frequently encountered in singing as opposed to speech.

I have the feeling, though, that it IS limited to American women, Gen-X and later, and especially to teens, possibly having come in when Valley Girl speech spread through the media back in the 80s. (And only, as above, when it's not an interior part of a phrase or sentence, but something followed by a pause.)

But I'm wondering if I'm way off base. I live and work alone, hardly ever watch films or non-sports television, and rarely talk to anyone I don't know, so I'm not really qualified to judge. And I have the vague thought that "cultured" English of the Cary Grant era had that same pronunciation, not limited to women. (Nor, for that matter, to the word "you". My Dad (b. 1926) always answered the phone "he-LEHoh"...)

Far more space than this was worth -- I've put it in the Writers' Forum because it might conceivably turn up in my Hannah Montana-in-1980 story if I can ever work out the logistics of that one, let alone write it -- but can anyone steer me right on this?

Thanks, Eric