VOCAL TECHNIQUE MADE SIMPLE
One of the frequent positions, of internal musical choice on voice that take some away from the development of their true voice is the refuse of something.
To make an example: those who totally refuse nose sound, in any way. They usually get to such a pure flat that takes away the sustain and as I said many times in my tutorials when you have not sustain you will have the sound of no sustain and in this case with correct positions they will sound truly nasal as they do not want. So avoiding the nasal resonances they are obtaining exactly to be stuck in the nasal sound any time they do not want to break the flat sound. So the correction is to put some exercises with correct nasalisation and develop sustain through that and yeah the nasal sound will go away.
Think about that anytime you are absolute in refusing a voice characteristic.