[Elecraft] Strange digital transmissions

[Vic K2VCO]

I've been hearing this lately on the low end of the 20m CW band. A noise 
that sounds like a distant machine gun. There's a burst a few seconds 
long, and then a response -- obviously from another station.

These signals are wide-ish, taking up a few kHz. The K3 DSP noise 
blanker reduces their amplitude a little but doesn't eliminate them.

I'm pretty sure they are not amateur signals -- they are not on 
'digital' frequencies, they are in fact too wide to be legal in the 
CW/digital part of the band, and they are very loud.

Does anybody know what they are?
-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco