Autumn flies

No pun intended!  Within the past month we have had large numbers of large
flies collecting in our windows.  I thought at first they were cluster
flies, but they are not, and are tachinids or something similar.  My second
thought was that we had something dead, but undetected, in our walls or
crawl space (no basements, as such, here on the Eastern Shore of Maryland.
One of my neighbors then reported that he had the same problem.  Do these
flies, although not cluster flies, have somewhat the same habits, or should
we both start looking for corpses?

Thanks, Mac