You mean clogging my nose with something or cutting off air kind of like squinting, but without actually wrinkling your nose? What I have most difficulty with is matching the pitch, I can't control my voice very well at mid-high pitches... I'm fine with high and mid, but the point in between(where Mustaine's sound lays according to my schematic) is rather tricky. I still get those teenager croaks once in a while.