Well, growling is quite easy when you know how to do it, but your first step would be to get yourself a drink, this could essentially be anything, juice, water, coke, beer, or even better: milk with honey (tea with honey could also work). Drink this when practicing and you won't hurt your throat that much. Second, you should clear your throat, grunt… this may sound silly, but don't worry, I'll get to the cool stuff right now, when you've cleared your throat and found the technique that gives...