I don't know exactly how to describe it, maybe like a gargle? The noise is not from the engine compartment, more like the interior center console/dash area. Kinda like irregular vacuum noises. Obviously this is only noticeable at idle but does go away when I turn the fan or system off.

What is this?

 

My car also started making this noise lately. Its due for a major service now. A tech told me its because the gas is low and needs to be filled and will be done during major service.

 

Possibly low on gas!