This thing is driving me crazy! In the past three or four days, it's appeared daily, sometimes as early as 7 a.m. ET (1100 UTC) and sometimes with a rather good signal. It comes and goes.
What is it? I only hear it in AM mode - I checked the others and got nothing. It sounds like two hollow blocks of wood (as in rhythm band; remember that?) being knocked together at a steady three to four beats per second. I'm guessing that the signal is vertically polarized. It can fade up to being the strongest signal on the frequency and then completely disappear in a flash, only to reappear again ten or fifteen minutes later.
What am I useing to hear this? Icom 706 and a half-wave groundplane (an old CB antenna) about 30-feet in the air.
America needs a sense of humor...