There's a certain type of vocals that really bugs me. It's an old fashioned warble, female vocalists seem especially prone to this. It's when a note is not held but instead the throat is vibrated. Examples include Susan Boyle / Wild Horses (an extreme example), Streisand, Joan Baez. I can only think they do it because they are terrified of being off key (flat or sharp). The "beautiful" voices don't do this - eg Alison Krauss. So, is this warbling an indication of a lack of confidence or a poor voice?