After driving to work this morning, I was smelling antifreeze. There was none leaking but I heard a strange noise under the hood. When I popped the hoid, I head fluid boiling in the coolant resovoir. Not the radiator, but the plastic resovoir. Do I need a flush and fill? Has anyone heard of this?
I had a similar problem.
It started when my car overheated one day after idling for a long time (parked). When I checked the coolant, there was none!!!. No puddle under the car or anything either. I refilled the Radiator, and checked for leaks. Found none. Been checking the coolant for almost two months now and haven’t lost any.
For a few days after this happened, Whenever I would get where I was going, I would hear the Resivoir “bubbling”. Not sure if there was air trapped in the system or what.
And I STILL can’t figure out what happened to the coolant in the first place!!! 
sounds like your radiator cap is not holding pressure…replace you radiator cap…I had the same problem with my LS and after I changed the cap it never did it again