Hello, TheOldHippie
This sounds exactly like the effects some military choppers produce. The ones I have in mind are designed to produce rather confusing and disconcerting noise so it is harder for people on the ground to react preemptively with a sense of direction. Military jets flying near the speed of sound produce a similar effect, but theirs is a loud roar that seems to come from every direction. Of course, choppers don’t create the effect I described by flying near the speed of sound.
Area law enforcement sometimes uses military help, including choppers. This is often done when military technology is used to detect marijuana growers with plants mixed in with other foliage. The military has photo reconnaissance that distinguishes between subtle differences in colors of green. Marijuana plants have a fairly distinctive registry of color.
Besides that, the evening you heard this noise military fliers may have just coincidentally flown some of these choppers over your area on the way to wherever. The pilots may have intentionally flown to produce the effects I described as a prank. I know some military fliers. They get bored fast, and they talk about pranks just like this.
