What Is In My Wall And How Do I Get It Out? [POLL]

This is the weirdest and creepiest thing I've encountered in my new house.  I have no idea what is in the wall of my living room but I can only assume it's a bat.  

I first heard this high pitched sound and scratching on the inside of my wall about two years ago and figured it was a bat.  The sound came from just below my light switch and has never moved.  The weird thing is I didn't hear it all of last year but, I heard it this morning.