I think you are right regarding the telemetry. I found out a bit more about the system - the repeater input is on 415.7875 MHz. On the input you only hear chirps every so often some may be 10 seconds to over a minute, and these chirps gets repeated onto 410.7875 MHz. They have a system called TRIMS or "Train Radio Information System" that is used for PA Announcements, Train Emergency Intercom, Silent Alarm Activation on the train, transmitting train Fault Codes (FC), and change the Platform LED Message Displays (PLEDS).
I am guessing from this information the chirps are broadcast in some sort of timed sequence from each station and/or train and contains data of the broadcaster eg. station ID or train ID along with some sort of status code or command. This would make perfect sense since listening on the repeater input is simplex and only the transmission local to my radio receiver is heard, but since the chirps out the output is continuous it must mean the rest of the chirps are coming from different places along the train route. If anything it is likely some sort of a ping saying something like "Radio ID 1234 with FC 0 is alive" back to the control centre.
At the end of PA announcements you would hear two chirps, one of them might be coming from the head end and the other from the train or station, like <End of Announcement Packet>, <Acknowledgement Packet>. Although PAs are on a different frequency, the data format of the packets are similar suggesting they are part of the same TRIMS system. The frequency pair in question is dedicated for data.
It would be really interesting to pull up a datasheet if the manufacturer of such hardware could be determined.