Overheating 22R Engine Thumping

My truck overheats, and when shut off, it makes a loud thumping noise from the engine bay, and the upper/return radiator hose flexes like air or coolant is moving through it.

Yesterday I flushed the radiator because of this same problem, and figured it was just time to change the coolant. At the same time, I replaced the spark plugs, oil and filter and air filter just as maintenance.

I want to say that it's air in the loop, but it was doing the same exact thing before I flushed the system, so I'm doubting that. I don't think it's the thermostat either, because coolant does flow when it's warmed up.

Also when it does the thumping thing, it usually (but not always) expels coolant from the overflow hose.

Thermostat wasn't opening up completely it seems.

Fixed!