About his voice, i think a important thing is "drugs"...
Remember that a big part of the Chester's insanity in the early years was thanks to the drugs. Just reading a couple of interviews from 2000 to 2004, and you will see a picture of that reality.
After his mayor problems with Samantha in 2005 he started a new life with Talinda. And a clean life, so, to me is important because now we have a "normal" Chester, with a "normal" voice, without being influenced with drugs, or rather altered.
Also guys, he is very young yet, but he is not 25, he is 37 now.