Dog and that danged wall

I turned in around 11:30 pm last night. The older dog curled up on his pillow in front of the heat register and the younger dog took her place on the foot of the bed. Sometimes she's a nice footwarmer. We had all settled in for a good night's sleep. I was sound asleep when all of a sudden I was almost knocked out of the bed by the younger dog who suddenly jumped from the bed hitting the floor a good six or seven feet into the bedroom and ran screaming bloody murder down our upstairs hall. I heard her hit the rear stairs still screaming. Strangly the other dog only looked disturbed. Wondering if someone had broken in, I armed myself and went after the younger dog who I could hear screaming downstairs. Those of you who own dogs know what I mean when I say "screaming". They are not barking, they are screaming. I went cautiously down the stairs where I could hear her screaming and digging frantically at that section of wall, beside the door from the dining room to the library. Needless to say I couldn't hear much of anything; it would have had to be thounderously loud to be heard over the frantic dog screaming only a few feet away. But I saw nothing amiss with the wall, other than dog scratches. I finally got her settled down. The wall is just the wall. I have no idea what she thinks is there. The other dog could not care less what is there. He didn't even come down and give me moral support. I looked at the mantel clock which read 1:30 am. Its a good thing I can usually go back to sleep easily; unfortunately my wife has problems going back to sleep.If nothing else this moron dog is going to ruin that section of wall requiring replastering. I really do not need to be suddenly awakened between 1 and 3 am by a dog with a wall fetish. Anyone with ideas please comment.