[50mhz] Name this sound

[David Kozinn, K2DBK]

This evening, I've heard a sound on 50.260 that I haven't been able to
identify. I'm not familiar with all the digital modes so this might be
something relatively simple, but I couldn't find a clip online that matched
it, nor could I figure out which of the many modes available in DM780 (part
of Ham Radio Deluxe) could decode it. The audio lasts for just under 30
seconds and seems to repeat after 30 seconds of silence, so I was thinking
it might be a weak-signal mode but it's very wide and didn't match anything
in WSJT that I could find either.

Rather than try to describe it, I've posted a full "cycle" of the sound up
on my website (since I didn't know if I could post an attachment here).
Here's the link: http://k2dbk.com/50.260.mp3

Can someone let me know what this is? Thanks!

73,
     David, K2DBK
     k2dbk.com
     k2dbk.blogspot.com