As a long-time resident of NW Washington, DC, I have sadly noticed a vastly increased number of helicopter flights over the neighborhood.
Caveat: my observation is purely personal, not based on scientific research.
I've of course called all the possibly "responsible" agencies for the unbearable noise produced by these 20th-century flying machines (mechanical super-bugs carrying a handful of [I assume] privileged people) during all-too-many hours of the day, asking myself why they're flying so noisily over our (supposedly peaceful) homes, but have gotten no satisfactory answer from any of them.
The most responsible response (but still not an answer to the issue) came from the Office of the Inspector General, FAA (1-800-424-9071). The FAA is supposed to have an answer to my helicopter-noise query by 3/23, if I understood the polite person I talked to there correctly. FYI, my helicopter-noise "complaint" to the FAA has been filed under DOT 1 60 302 15.
If you are experiencing the same helicopter noise-bombardment syndrome, you might wish to call the above no. (1-800-424-9071), citing the DOT no. also mentioned above (DOT 1 60 302 15).
Or, you can buy ear plugs. But they don't work very well. :)