A very present and insistent whistling at night.

I don't know if I'm overreacting or looking too much into this, but I have been hearing a very present and rhythmic whistling sound at night when I go out onto our patio.

My husband and I like to indulge in cigar smoking. The first time it happened, we were both sitting outside having a smoke, and heard it in the darkness. It was rhythmic. It was like someone was trying to whistle a specific tune.

We went to check itt out and found nothing.

We don't live in the city, but we also don't live in the countryside either. It's kind of a middle ground. We have neighbors, most of whom are elderly, but our houses are also spaced apart by a significant distance.

My husband has been at a work conference for the past few days. I went out a couple of nights ago for a smoke and heard the same whistling sound. It came from the other side of our garage. It would whistle and then stop once I poked my head out to check it out.

I checked it out, but without the safety and security of my husband's 6'2" frame, I did so with my LED flashlight and .38 special. Again, nothing.

The last time I heard it was last night, but I actually heard it through the window. I was charging my tablet when the whistling started. I wasn't sure if I was hearing the whistling, or if I was imagining it.

Anyways, I decided to stay with my brother until my husband gets back home.

Also, we do have security cameras on the outside of our house. Nothing fancy, but they get the job done. I checked the feed and saw nobody. It is worth nothing, however, that there is a blind spot between the garage and the fence. It isn't likely that anyone would be able to get out of this enclosed area. If they did, they would have to jump a six foot fence, which they probably wouldn't be able to do very silent&my.

Anybody have any theories?