We've only been living here a month, and already we have guests. They're in the walls upstairs, I think. We hear them most in the morning, as they're getting ready to go to work, scratching or building; the mother making bag lunches for the kids. I checked up in the attic but didn't see or hear anything. But I know how good they are at keeping quiet. I'm guessing mice? Squirrels? They don't seem quite loud enough to be squirrels. It's a kind of a gentle scratching, almost like a muted pecking.