Yep. Fax spammer. They call my land line, which is not hooked up to a fax machine, and the answering machine gets it. I get a nice L-O-N-G message of beeps. I've gotten similar fax spams in the past (all to land lines, all without a fax machine on them). Often the calls come in batches, especially when you pick up by accident or just to stop the beeping. Once -- and only once -- I hooked up a fax machine to the line in anticipation of the follow-on redial, and it turned out the important fax was a stock tout urging me to buy a pump-n-dump stock. I have no idea if these nit-nats are doing the same thing, but you have to wonder, when fax is a dying technology, what they think they have to gain? I suppose the other folks who've said they send blank faxes should realize that the fact that they RECEIVED blank faxes means (to the sender) that there is a live fax machine hooked up at their number.
I called the number and it was a personal cell phone number owned by a woman in Colorado. She says she does not send faxes. The entity is using a "bogus" number when sending those faxes.