Each time I start the engine when it's cold or cool, I hear my coolant making a cavitation sound from the heater core. This is caused by air being trapped in the core, and the noise stops after I drive the car a few miles.
I have checked my heater hose orientation, replaced all hoses, the heater coolant valve and engine thermostat. There is NO loss of coolant whatsoever and the heater core is OEM and not leaking.
The heater coolant valve vacuum function is correct, and the heater puts out the proper amount of heat. After the engine has been run to speed, the cavitation sound is no longer heard.
My question is where might this trapped "air" be coming from (head gasket issue?), and what is an effective way of bleeding it from the cooling system.