I find that certain singers, in trying to prevent an accent, have a very articulated way of pronouncing words while singing.
Tarja Turunen, Klaus Meine, Agnetha & Anni from ABBA. All of them have strong accents while speaking and Klaus' comes through the most while singing, but not strongly.
I tend to think that the act of singing powerfully has an equalising effect on voices, and that when a strong regional accent is obvious it is that
which is an affectation.