If you cough then you are using too much of your throat. You have to figure out how to draw the air in from your guts. Imagine that you were in a room full of poison gas and were on your last breath before you found an oxygen tank. Now just how big of a breath do you think you would take? Focus that amount inward while drawing it steadily across your vocal chords. Use as little air as possible but use maximum force. It's really hard to explain from there on how to go apeshit with just a fraction of a breath. I suggest trying excercises where you try to breathe in as slow as possible and see how long you can get at drawing in a breath. Try inhaling for 10 seconds uninterrupted, then 20, and then 30 if you can without trying to growl. That should get you used to inhaling. Then after you got that down, add a bit of your throat and if you screech then you need to relax your throat while applying the same pressure if that makes any sense. Eventually your throat will loosen up and you will get used to it. Granted, when you do it your head feels like imploding but hey, I feel like I need an Advil after each song I sing live normally so that is no biggie!
Hope that helps.
