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They probably brought something home with them. It happens.

Is there any known history with the home? Prior owners, deaths etc..

First poster got it right
If  they(grandparents) were going to voodoo doctors, a spirit attached to them. Or if already had a spirit attached to them, the voodoo opened something up.

Did your grandparents also go to Tarot card readers, spiritualist, etc... It would be my guess they did. They probably had many spirits attached to them.

My grandparents had a spirit, ghost, whatever in their house. I remember seeing doors open and close by themselves, heard footsteps upstairs when nobody was there, I actually have seen items move and even levitate.

The house was a rooming house around the turn of the century and the story was that a guy who was a barber in town lived in one of the rooms upstairs. One day he had a heart attack, ran downstairs and out the door on the side porch where he died. I have even heard footsteps running down the stairs and the door to the porch opened by itself.

The old house was torn down after my grandparents passed and my mom sold it. It's now just a vacant lot but Grandmama's fig tree is still there. Maybe the barber is at rest now.

When my father died, my mother asked me, my ex and our son to move back home. I agreed; mostly because the house/property were too much for her and hired help was taking horrible advantage of her.

What I could never have imagined was hearing my father get out of bed to use the bathroom - every night until my mother passed, ten years later!

My bedroom was under theirs and I had heard that sound (those footsteps) over my head, nearly all my life, growing up. There is no doubt in my mind what/who it was and the fact that it stopped the very night of my mother's passing confirms it, as far as I'm concerned.

They should both be at peace now.  

My wife had heard of a similar case where the FIL of the lady telling the story hung around after he passed. He was waiting until his wife passed and then presumably they left together.