Remove CO detector From wired alarm system
I solved this by re-inspecting the detector that was making the noise. I discover that the original wiring had reversed white and black power connections.
Perhaps the older alarms were not polarized.
I have no confirmed idea why the external CO detector impacted this system, my theory is it helped balance the load to offset the crossed wires.
After fixing the wiring, I was able to remove the external CO detector without any further issue.