Our (U.S.) time signal is at 60 kHz, On my Lowe HF-150 get it at about 59 kHz in USB mode, and almost 61 kHz in LSB mode. That's an amplitude modulated signal also. On other receivers the USB/LSB offset might be flipped. If the beacon you're wondering about comes in strong enough, then you should hear its pulse right at 66 kHz in AM mode, but it won't sound like a beep. It would sound more like a low 'buzzing' pulse. But the carrier has to come in pretty strong to hear that.
To further inquire about this UNID, you can go to Longwave Home Page
, look for the tab that says "messages" and then post. You don't need to register. Somebody else may know what it is.