Government? Military? Encrypted? Spooky?
The most likely cause is.....a CB'er. Next is some mode you aren't familiar with.
Freebander? Some doofus operating a heavily modified CB radio and/or a poorly built and poorly tuned homebrew linear amp? CB band is directly below 10m. Or it could be one of those Latino or Russian taxis that are illegally using 10m. I believe the taxis are using FM mode. There was a recent IARU report on QRM from illegal 10m two way radios apparently used for taxicabs, most seem to be in Russia and Latinoamerica. I dunno who is mfg'ing those systems, Russia still has an electronics mfg sector so the radios could be being made in Russia and sold in FSU countries and to Latinoamerican taxi co's, Russia has historically been close politically and economically to many countries south of the Rio Grande. The Bolivar Bloc, which consists of Venezuela, Argentina, Bolivia, and Cuba, has active trade and political relations with Russia. I heard long ago that Russia has experimented with phase modulation, something never used in the West. The taxi radios could be using phase modulation, if not FM.