It could have been a giant Red Head Centipede. Depending on where you were living at the time, Centipedes can grow upwards of 8″ and they make that exact scratching sound as they scoot underneath papers and against walls. I know by experience, however, I had to get out of bead, find the creepy-thing and then – kill it. Problem solved. No more scratching sounds.
Barn Sour Pony