Dr Ray Stantz: "Symmetrical book stacking. Just like the Philadelphia mass turbulence of 1947."

From American Libraries Magazine:

Haunted libraries fall into two types. First, there is the “building with a reputation,” where a convenient murder, curse, or other tragedy has occurred. Library staff can then blame the odd noise, the occasional book falling off the shelf, or glitches in the air conditioning on the resident “scapeghost.” No one reports anything too spooky, and the children’s librarians have a good time with it at story hour. 

Second, there are libraries where credible, responsible people observe enigmatic human shapes, hear disembodied voices, and witness other classic parapsychological events. Glib explanations about how the building must be settling ring about as hollow as those mysterious footsteps late at night on the upper floorboards. The library staff learns to live with its wraith, usually by accepting the paranormal as a normal working condition. 

Both categories of haunted libraries are described here...