Probably due to a desire to sound cute or otherwise I find teens (girls mostly) using an accent wherein they have to pout their lips a bit more in speaking while this may give them a more appealing look or peer group acceptance the accent changes; moreover this is not a localised phenomenon but spread out throughout the age group.
Has this ever been noted?
Which are the cultures wherein the accent changes with demography?
eg for an adult it might be p-aa-rty the teen says ph-o-ty (with a flapping of intervocalic /t/)