The heater tubes/pipes run through the firewall and under the dash. It could be air in the system. The coolant would be circulating when the engine and heater is on.

You can open the hood and look where the heater hoses go through the firewall. This would give you an idea of where the heater core is located.

 

Appears CoolBlueSS is correct, get under the dash, remove the panel cover and have someone operate the controls for Heat/AC, blend door is being held up by something, seal around opening may have come off or deterioratedshouldnt of, not that old but could have. Most likely the door by the passenger kick panel.... Jeff

 

The gurgling I had was due to bad head gasket along with stripped head bolts. Maybe the gasket was good either way it was leaking coolant. Fixable using NS300L Head bolt repair kit.