Screaming or howling in Pulaski County, Arkansas

In October 2010 I was bow hunting on Camp Robinson military compound in North Little Rock, AR on Approximately 23,000 acres. I was hunting between two mountain ridges in the bottom of the valley approximately 100 yards from a thick creek bottom. I started the afternoon hunt at 2:30 pm finding my way to a new stand set up. I hunted all afternoon seeing alot of good deer sign in the area. After what started to be a promising day in the deer woods. I did not see a deer all day and the sun starting going down behind the mountain ridge to my west. It was getting so dark out that I could no longer see thru my peep sight. So, I decided to start packing up my backpack and start my decent down the tree. By now, it was well after dark and without my headlamp I could not see 3 foot in front of me. As I started to make my way down the tree. I heard the most disturbing sound in the woods that I have ever heard in my life. It was a very, very, loud, deep toned, gravely, blood curdling Growl/yell which seemed to be approximately 150/200 yards away from me to my southeast. It sounded as if someone was trying to yell for help. I immediately froze to the side of the tree and tried to gather my thoughts on what it could be. I originally thought that it was a person in the woods trying to play a prank on me. Mainly, because I had seen a pickup truck drive down the distant ridge several hours earlier. Then I realized that it was too loud to be a human screaming in the woods. I remained frozen to the side of the tree for several more minutes and tried to gather my thoughts of what could have made that sound. I am 43 years old and have been an avid hunter every year in some capacity since I was 6 years old and I have never heard anything like this in my life. After several minutes I finally made my way to the base of the tree, packed my stand, grabbed my bow and started to walk out on the trail that I walked in on into the direction of the "sound". I had about a 50 yard SE walk towards the "sound" then 100 yards west to an old logging road then 300 yards north back to where my truck was parked beside a small pond. So, as i left the tree walking SE and arrived at the west trail. I got a very uneasy feeling like something was watching me. So, I stopped to listen. Its was then I heard the "sound" again. It appeared to be moving closer to my location and approximately 50 yards away. Needless to say, I did not stick around to see what it was, for all I had was a headlight, bow in hand and a gut knife on my hip. So, I immediately start sprinting toward my truck. I have NEVER been so scared in my entire life. I started my truck and got the hell out of there. On my drive out of Camp Robinson. I called several of my closest friends and my dad and told them of the encounter. I stayed up all night on the internet to research this sound that I heard in the woods that night. I listened to mountain lions, african lions, tigers, bears, bobcats, foxes, coyotes, wild boars, etc... and I could not find anything that would come close to what I heard. The very next day. I drove back to the same area at Camp Robinson where I heard the "sound". Again right at dark from the comfort of my pickup truck with a pistol in my hand. I heard the sound again further down the valley approximately 1/4 to 1/2 mile away. I was a very distinct sound, very loud.... Since, these three occurrences. I have hunted at Camp Robinson on many more occasions and I have not heard this "sound" again. Still baffles me to this day of what I heard those two nights and I have still never heard anything like it.