Thanks, Gaga! I'm not on Facebook very often, so I missed that. One of the commenters seemed to think it was Barrett Selcall which does sound similar, except it uses the more common 170 Hz frequency shift, and transmissions last about twice as long as these bursts.
I assume it's some sort of organized system of transmitters. Transmissions were all the same duration, and when there was more than one signal at once, they began roughly at the same time similar to FT8 or JS8Call, but with longer pauses between frames.