Digging and Scratching noises

Last night we turned in about 11:30 pm. My wife went to her bedroom in the east wing of the house (She has a leg problem which requires frequent monitoring) and the two dogs and I went to the master bedroom. The dogs and I romped and played for about 30 minutes to tire them out good (I'm usually the one who is tired out). We all settled in for the night. The older dog took a position at the foot of the bed, made three turns and flopped down. He rarely stays there more than an hour or so, after which he jumps down and goes to his regular bed on the floor next to the heat registers. The younger dog takes her place about midway on the bed and pretty much stays there unless thunder is heard or the night turns cold when she moves toward the head of the bed. Last night I had just about dozed off when I was awakened by frantic digging and scratching noises. Dogs digging the covers is a definite no-no and I thought I had them broken of the habit. Because the sounds came from toward the foot of the bed I naturally thought it was the older dog digging up the covers. I yelled at him to stop. Looking toward the foot of the bed I could see him lying there looking at me as if to say "Stop what?" He was not digging and the younger dog, much closer to me was sleeping through it all. So neither dog were reacting to the digging noises. That is strange. I turned on the light beside of the bed and the digging sounds immediately stopped. The phantom digger has dug me awake before. There is never any sign of the digger or the dug. The dogs seem to ignore the sound though it is rather loud (if you have a dog who digs the carpet or blankets you know what I mean). I really don't think mice would dig that loud. If we have rats I'm not aware of it and besides I think the dogs would react to a rat. So what causes these sounds in the middle of the night? Another old house mystery.