I went to get some Seafoam and put that through the system. In the parking lot, I decided to pull the vacuum line off of the control that goes to the butterflies in the manifold runners. It looks like an EGR valve mounted to the back of the manifold and has a vacuum line and electrical connector on it. The ticking stopped immediately
Put the line back on and it slowly came back. Went and did my shopping, came out, and started the truck, ticking was there. Pulled line and it instantly disappeared. I drove that way for about 15 minutes and no ticking was heard at all (engine light did come on, but that should reset). Plugged the hose in and it came back.
So in my case it was not a valve, lifter, or injector. With that noise gone, I could hear the injectors and they are relatively quiet compared to the noise from before.
So my question is - what is the cause, does it matter (can it cause other problems), and since the truck runs great, should I mess with it?