Weird OS X problem

About a month ago I backed up my iBook's internal drive to an external drive (my 20 Gig iPod, actually). Now, for some reason, the "Volumes" folder on my internal drive has a mirror of the backup. When I erase it, it shows up again the next day. Seems to do it every night at 11 pm, in fact. Anybody know what the heck is going on, and more importantly, make it stop? First person to give me a satisfactory solution gets an iron on of one of my drawings. Discuss