Mystery of the Gurgling Heater Core

The heater core on my 1998 Dodge Ram was gugrling air on startup, sounding like a percolating coffee maker when I would start the engine in the morning. I approached the problem by purging the system of air and then searching for a cause after that. The heater core was noisy but it never leaked fluid. This is not an instructional video and I am not a professional mechanic. This video is published for entertainment porposes only.