attack of the flies

Last Wednesday, Lot and I got to my house and there were 4 flies hovering around the chandelier. I thought, "why are there hella flies in my house?" I was a little embarassed because I was thinkin OG, what is Lot thinking right now.. that my house is dirty? haha.. Anyways, I killed those big ass flies... but then what do you know, after killing 4 flies, there were 4 more... And the more I killed the more came out!!! At the end of the night, we must have killed at least 20 flies!!! And ask Lot, I AM NOT EXAGGERATING. It was crazy and unbelievable... I checked the windows everything and there was no opening for them to get in....

Lot's theory: There were maggots in the chandelier.
I checked the chandelier and there were no maggots.

Jason's theory: Something died in the chimney and the flies are coming in through there.
I checked the chimney, there is no dead animal and the damper is closed for any flies to get in.

Archie's theory: A cat died on the side of the unit and flies are coming in through the side window.
The window is closed and no flies can get in through that side. There is also no dead cat.

My theory: They're coming in from the vent.
Have not seen come out of the vent yet.

So WHAT THE HELL IS GOING ON? The next morning, before I left for work, I saw one fly. Okay, just one.. Not a big deal. But when I got home, there were 3... Then I killed those... But more came.. Total killed (with Archie's help) -- 7.

So today's another day. Before I left work there were none to be found... I'll pray that they're gone.. but if they're not, I really, REALLY need to figure where the HELL these big ass flies are coming from...