I would say firstly to go find out the history of the house to see if there are any clues within that, Keep a log of all that happens that seems odd
ect..
You also need to look into ways to rid any not so nice spirits in the house,
If any one in the house ever feels in danger of this unknown force make sure they imagin a bubble of white light around them as this protects... A
good idea is to do this each morning,
Also invest in some crystals to help keep the calm in the house,
Im sure other ATS members will have ideas for you....

