Gurgling Sound, Gurgling Sound coming from under my hood. Options

[5150EVH]

I recently noticed that when I come to a stop, I hear a gurgling sound coming from behind my firewall. I only hear this sound hear and there. I noticed too that when I turn my heat on the sound goes away....however, I smell a whiff of antifreeze when I first turn on the heat. I have been in the automotive business for 4 years (manager at Autozone and with CarQuest) and know that usually when there is overheating or this type of symptom and you turn your heater on and the problem goes away...its usually the thermostat. I was just wondering if anyone else has had this problem or if anyone could please give me some advice. I would greatly appreciate it. Thank you.