Our pest is the Wisconsin Ground Squirrel, also called the striped gopher. It turns out this little guy was just looking for a warm place to spend the winter. He never made it into the house, but was in the downspout and the scratching noise was him trying to make things cozy.
We were able to solve the problem by putting screens on the downspouts to prevent the critters from getting into them. No more scratching noises and nothing has been caught in our trap. Everything is good.
Usually these little squirrels are pests in the garden, enjoying roots, bulbs and other delicacies. In the springs it is pretty obvious if you have these visitors. You will find little trails dug into the grass as well as little burrows about an inch and a half in diameter.