[Lowfer] HF data burst

[Dexter McIntyre W4DEX]

For probably over a year I have been hearing on multiple HF frequencies 
what sounds like a momentary burst of 4 data pulses.   It often repeats 
every few minutes then either quits or moves frequency.  A sample just 
recorded on 60 meters at the link below:

http://www.w4dex.com/hf-data-4pluse.wav

I don't believe it's local as others at a distance have reported hearing 
the same.

Any idea what the source is?

Dex