All of the 851-854 MHz interoperability channels are actively in use in Mexico, so nothing in San Diego or Imperial has been reconfigured. You are either hearing that, or something up your way.
As I recall, Riverside County is putting in "back-to-back" repeaters (ITAC1 linked with 8TAC91, for example) at some of their sites. Could be them or one of the other Basin counties.