No split personality (afaik), just constant struggle with a bad case of sore throat - that's why the vocal tracks are different from one song to the next :) Thrash metal is not about growling/grunting like a wounded baboon, it's about revolt, energy, protest and making a stand in general - if ppl can't hear what the heck you're singing (talking) about, the message gets lost :) That's why most thrash bands go for the shouted / barking / melodic type of vocals.

Kudos for the comment :)