Do you have anything in your home that has rough edges, say like the side of a crate or under a table or something. Since it happens frequently check out her favorite places to be first.
thats a good idea, we do have a lot of crates and such(4 in the house, 1 in the van) I will have to check the piggie room and my room, that is where she spends most of her time, standing there staring at the critters lol maybe Kari jumps up and bits Happy during the night

It is also possible that dogs know when you are not near, is there any chance they may be great together when you are there, but when you sleep they rough house.
not really no, they are not allowed loose in the house without supervision. and we make it a point to keep perky and Happy seperated when no one is watching. at night Ripley, Happy, and Misty sleep in my room with me(door closed) , Ripley and Misty both sleep under my covers and pressed up against me, Happy sleeps at my head. in the morning mistying and Ripley roughhouse on my bed, but before they ever wake up Happy is already on the floor staring at kari