Ego
Well....given your choice of screen name
I'm not really sure how serious you might be......but two answers come to mind.
1-Ask your teacher!......easily possible that any answer we might give you will be a re-tred of what your teacher will say.
Also possible that anything we might tell you is 180 degrees from what your teacher is going to say.
Since your NOT taking lessons from any of us (presumably) what any of us say is largely beside the point for YOUR practice.
2-The "stock" answer---or one of them anyhow
is that such a loud yell--I presume you mean a kiai is simply part of the practice......people often "grunt" or forcefully expell air when lifting heavy objects---at least the powerlifters that work out in my gym do!......Boxers often "huff" a quick breath when hitting/striking the heavy bags........my guess is something simlier.
If your running out of air that is a whole other story......if you not then my best advice is again, ask your teacher and try not to let such mundane things worry you.