Helicopters circling overhead - I guess this is the right place to ask?

Several times a month we have helicopters circling overhead, no, not directly over my house, but in probably a circle about 1/2 mile diameter. They just keep circling and circling. This goes on for about 15 minutes to a half hour.

There is no spotlight on, it's always at night, about 10PM. They are long and black as best I can tell at night with what ambient light there is and have an exceptionally bright red light on back. There are no sirens or anything in the neighborhood, it's a very quiet place, but just the noise of this quite loud helicopter circling and circling in the same pattern about 200' up. At first I thought nothing of it, but now it's repetitive I decided to ask. In local posts I've seen others occasionally wonder too what is going on but no answers. Any ideas?