Screaming or howling in Brown County, South Dakota

When I was a senior in high school (1986), I was staying overnight at a friend's who lived about 8 miles north of the town where I lived, Aberdeen. It's very flat in this area, although it does start to get somewhat hilly just to the north of where my friend lived--very few trees, just miles of open farmland, and very little population. He lived on a stretch of gravel road that extended about 2 miles west off of HWY 281, and there are a few other farm houses along the same road. My friend and I were sitting in his basement talking until it was quite late--about 2am. It was a very nice spring evening--nice enough to keep the basement windows open for fresh air. We were both getting pretty tired, and we were trying to talk somewhat quietly so as not to wake the rest of his family upstairs. At some point, we heard some sort of screech or scream, and we both stopped and looked at each other, wondering if we would hear it again. After a few seconds, we heard it again. My friend had lived in the area all of his life, and he said he'd never heard a sound like that before. It sounded like it was coming from 50 to 100 yards away, so we both went to the basement window and looked out. It's very dark in that area, with no streetlights to speak of, but the moon was lighting up the surroundings somewhat. We couldn't see anything, but the sound continued for probably 10 minutes. It was a very strange sound, and I couldn't identify it as anything I had heard before. I asked my friend if it might be a fox or possibly a deer in pain (it sounded almost like it was in distress), but he didn't think it was anything like that. I can't really describe it...I just remember thinking that it was strange that we couldn't pinpoint what it sounded like. What was really strange is that my friend was quite the outdoorsman, and he was very used to the sounds around that area and attuned to the wildlife, but he was completely stumped as to what could be making the sounds. It sounded like whatever this creature was, it was howling or something, but it was definitely not a dog or coyote, since I have heard both, and it was definitely not any kind of farm animal. I had been a Bigfoot buff since I was a little kid, and I tried to tell myself it couldn't be one of those! But the sound continued for a while, and then it stopped. I had a somewhat hard time getting to sleep that night as the sound was still in my head, but after the initial 10 minutes, we didn't hear it again. If I remember correctly, we made a half-hearted attempt the next day to go see if we could figure out what had made the noises, but we didn't find anything (not that we looked very hard) I kind of forgot about the incident until I read some of the stories on this site, and thought I might report it. I have no idea what it was, but it's kind of a strange story!