Hi,
Wasn't CW though, the AM carrier was steady as a rock other than the odd fadeout

Another way to describe the sound is if you have ever been into V/ULF listening, it sounds like the "dawn chorus". The signal persisted for as long as I was awake (I listen laying in bed most nights

).
I thought of an outband HAM doing SSTV, but I've never heard such an emission on an AM carrier. I can pick it out on SSB OK though. There was the absense of the definate sync blips, but that could be due to the AM carrier noise making it.
Given some pirates have been experimenting with the low bands for the winter, I thought maybe someone here could lay claim.
Peace!