I used to rent a tiny in-law cottage behind a house across the street from the Brookdale Lodge in Brookdale, California. The lodge is supposed to be haunted. I've been there several times and never saw anything weird. Here is a link to the story of the lodge.
I do not know how old the cottage is, but you could tell that at one point someone added an extra room to be used as a living room. I almost never went into the living room area because it was creepy and dark, even though the room had a skylight.
In late April of 2001, I went on a one-night mini vacation to Lake Tahoe. Before I left, I cleaned the house very thoroughly so I would come home to a clean house.
When I got home, there were over 100 large black flies flying around the skylight in the living room area. There were no other flies anywhere else in the house. The house didn't smell bad. There was no food left out. Also, it was night, so the flies were not attracted to the skylight because of any light.
I got out the vacuum cleaner and used the wand to suck up the flies. When I emptied the vacuum cleaner, there didn't seem to be any flies in it. I just figured that they were coated with dust and debris.
I didn't think much of it until years later when I saw the remake of The Amityville Horror. I didn't know that flies were in some way connected to paranormal activity. I lived in the cottage for a year and have had some other strange things happen but nothing as strange as the flies.