I had this happen to me at my business. I live in a very small town, less than 2000, so I personally know the guys that work on the lines.
I was getting LOTS of them, I mentioned it to one of the guys I know, he said he'd look into it. He also told me, it was most likely the computer testing the line, BUT, it was not supposed to cause a ring.
Anyway, it turns out, that there was something wrong, some circuit, I don't remember exactly. After that was fixed, the calls dropped dramatically.
On a humorous note, as soon as the "Do Not Call" started, I signed up. I got a call, from some alleged vendor I'd never heard of, and told her, I was reporting her company. Then hung up.
I can still hear her saying, "Wait......wait.........."
Phil