I've replaced the heater control valve, but unfortunately, I've still got a leak there on cold start. Seems to be coming from the place where the lever is. Only leaks a little bit and then stops. There is a vaccum line that runs to the heater control valve - I'm wondering if that could be part of the problem - there really isn't much else that can go wrong with a plastic tee.
Since the truck has been able to hold cooant level, the ticking has ceased completely.