Mitchy,
I believe you're hearing coolant gurgling through the heater core of the HVAC system because of air bubbles.
The fix is to raise the front of the car so that the radiator is higher than the heater core, remove the radiator cap, start the car and run it to normal temperature with the hvac set to maximum heat. Then add 50/50 mixed coolant to the rad as trapped air bubbles burp up through the rad cap opening. Continue until no more bubbles can be seen, and no more coolant can be added. Once all of the air has been burped out, you should no longer hear the trickling noise inside the car. I've been there with a past OBW and this solved the issue. Good Luck!