Fax Machine Type Sound, Continuos Calls

Got this call twice on a phone number that only classified people should have.

Calls twice a day, between 11 AM and 5PM, does not say a word, does not leave a message. I just ignore him.

I call this number but nobody answered

Our unlisted home ph number has been on the National Do Not Call Registry for several years. This ph# started calling our number several months ago and the frequency of their calls is increasing. They never leave a voice mail. When I answer, no one is there or maybe I don't stay on the line long enough for a recording to begin. They call at all different times of day and night. I found somehwhere else on line where people complaining about this number say it's a loan company offering out loans or something. Then others say that no one is on the line. I also read when others try to call the number back that they cannot reach anyone. It's a nuisance. The number does not abide by the Do Not Call Registry.