What I would do is set up a a voice recorder where the most activity is comming from and review what you have captured, that way you can actually say I have evidence for whoever does a investigation on the house and compare recordings, I would also video record this as well but, make sure the camera is stable and noone in the house not even animals in the house if any at the time of the recordings, that way you can rule out manmade noises. If you cant or feel that your equipment might get harmed then I would set up a time and date to have Jim and few members of the group to investigate.