Have you checked the intake manifold gaskets? They are common to fail on GM V6s from the periods and they can cause mystery coolant leaks. The light-brown gunk in your radiator is probably oil, you can also check for moisture in the oil by looking for that same gunk under the oil cap, or even just water under the cap. Any of those things would indicate a leak in the intake manifold gasket. If there is a leak, you should get it fixed soon because coolant in the oil can damage your engine internals (bearings in particular), and oil in the coolant can clog your radiator, heater core, and coolant passages, leading to overheating.
As for the ticking sound, my Jimmy does it too, with only 97k on it. It should be okay, as long as it goes away quickly, but it can't hurt to run a cleaner through the oil next time you change it. Hopefully that'll loosen things up.