My bet is exhaust leak, or more likely an injector, or the vacuum switch on the intake manifold (not sure what it is called, but the one on my Metro sounds just like a lifter, or noisey injector)
Feel around the modules installed on your intake, the one making the noise can be felt to vibrate in time to the ticking. If you find a switch is ticking, remove the wire connector from it and see if it stops.... The idle can be erratic without it connected though. I still haven't broken down and gotten an OEM FSM for my Tracker or my Metro, so I am a little blind on the various modules and switches, when it comes to actual names and functions. The one on the G13 is next to a vacuum switch also. Not sure on the G16