This appeared to be war dialing. Call came in at 3:11 am, caller ID said Colesburg, IA. Filed a complaint with FCC http://www.fcc.gov/cgb/complaints_tcpa.html, others on other sites stated they received junk faxes from this number.
Receiving calls during early morning hours. 4:20 AM was the most reent. Just a beeb, beeb beeb is heard. May not hear from this pest for weeks or even months.