Get a PROFESSIONAL to look into it! Where do you live? In Tucson, AZ we have problems with Pack Rats! They destroyed my friend's house. Ate through wiring and everything. Had half the crawl space in the attic filled with stuff.
I also had a neighbor who had squirrels in the crawl space. They did a lot of damage too. Ate through the ceiling. Get it checked ASAP!
But - if it's ghost... You know who to call -
Ghost Busters!
