Hi Madeline Ann,
Did they say it was low on coolant? Also, have there been any recent repairs to the cooling system like a radiator, thermostat, or water pump? Or just had it serviced (drain and fill)?
There is a chance that the heater cooler is the issue but normally this is caused by air in the system and the gurgling noise is the coolant filling the empty space. One would assume that this is caused by a leak but that doesn't mean it is in the heater core.
If there was a recent service done, they could have left an air pocket in the system that could cause this.
The proper way to figure this out, is to pressurize the system and look for a leak. If the heater core is leaking, then they will find coolant in the HVAC housing. As you stated, I would hate to see them replace the heater and not fix it because it is not cheap.
Let me know if you need more information and we can go from there.
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Monday, June 3rd, 2019 AT 7:12 PM