Noises.

I am hearing scratching noises, either outside the wall, inside my wall or on the roof. I cant really tell. It is annoying and kind of freaking my out... especially if it is inside the wall. This isnt the first time ive heard it... about a week ago i heard it for the first time. What the heck is out there... or in there?!? I hope it is something outside and not inside. Ewwwwww.