Gurgling sound from behind the dash

Banana Republic 1

In recent weeks I’ve been hearing a gurgling sound from the dash. I’m assuming there’s air trapped in the cooling system / heater core cause I’ve checked for water trapped on the engine side of the fire wall. The car is a 08 B7 A4, the coolant is a small bit low, between max and min. If I top this up a leave the car idle from cold with the reservoir cap off will this sort it or do I have to go at the bleeder valves on the flow/return at the firewall. Currently there is no problem with overheating or getting up to temp.

Banana Republic 1

Any advice, no 🤔

Atlantic Dawn

Had this before directly after I made a coolant flush and change, it was like a sloshing noise, I thought it might work itself out but after 2 weeks it didn't, despite being at correct level. I ran the car cold with cap off idling and eventually air was gone and noise stopped, topped up when done. Took a few goes for it to work. What is odd in your example though is why it's happening out of the blue.

Banana Republic 1

https://www.boards.ie/discussion/comment/119361452#Comment_119361452

I don’t know, the fluid had gone below the max level about an inch. I don’t notice any leaks where you say air me getting in. Have looked at the bleed point and am not convinced there isn’t a tiny part of that that is covered properly. Theoretically could be the head gasket going maybe. 🤔👀