Screaming or howling in Missoula County, Montana

It has been awhile since this incident happened (1989), but I remember it well. The incident occured during the summer of 1989. I was working in my father's woodshop when my older brother (19 at the time) burst through the door. He was nearly out of breath and very distraught looking. He immediately demanded that I come outside right now. I asked him what was wrong but he just said, "Come out here right now! Quick!." I hurriedly followed him outside. It was late afternoon and the sun was just beginning to wane in the deeper parts of the forest. I asked him what was the matter. He told me to sush, and said "listen!" I could here that our grandparent's dog was going berserk. I could also recognize the bark of our dog in the distance as well. I asked my brother what was going on with the dogs and if they were fighting again. He said, "SHHH! Not the dogs, listen!" We were both silent, I didn't here anything. I asked him what I was supposed to be listening for. He said he heard something really weird, really freaky. I asked him what it sounded like. He said he could'nt really explain it, just that it sounded really weird. I told him that maybe he heard a mountain lion, as I had heard them on several occasions. They make a really strange sound like an inhuman woman screaming bloody murder. He said it didn't sound like a scream. He took off running down the road towards our grandparent's house calling for me to follow. I ran after him. Halfway to our grandparent's house I heard the sound. We both stopped in out tracks. I yelled to him "What the hell was that?" He excitedly replied, "That's the sound I heard, that's it!" I had heard a lot of strang sounds growing up in the deep woods over the years (elk mating calls, ruffed grouse beating their wings, coyotes, etc.), but never anything like this. I can't really describe the sound except that it was a high-pitched tone from a living thing that was very resonant, powerful, and well controlled in its execution. It made the hair stand up on the back of my neck. Soon, whatever it was out there in the woods ahead of us made the sound again, this time for a shorter duration and slightly broken. Another period of silence (other than the dogs going nuts). We continued running towards our grandparent's house. We soon arrived where the dogs were. Our dog was standing next to our grandparent's dog which was tied up. They were both looking and barking into the forest in the direction we had heard the sound coming from. I had never seen them bark like this, not even at bears. All of sudden, we heard a similar sound come from a completely different direction of the woods on the opposite side of us. Immediately the call was answered by another loud report where we originally heard the first sound. Whatever was out there, there seemed to be two of them and they seemed to be communicating. We continued to listen. Nothing for a minute or two. Then we heard two more distinct calls, this time from the same general direction in the woods, yet seperated. They were now coming from a farther distance. Again they seemed to be replying or communicating to one another. We continued to listen for several minutes, but the sounds did not occur again. We told our family members about it but no one really paid much attention as they had not heard the sounds and since we lived right in the middle of an area used by bears and other animals to travel through the wilderness regularly (the tribe caught 7 bears in one summer using live bear traps near our house!) they probably assumed it was just some animal out in the woods. In any case, I have never forgotten the incident and often think of the surreal event every time I go back to the wilderness.