Hi. Such sounds aside, I'm wondering how the coolant is flowing out of the overflow chamber -- where is all the extra coolant coming from? Your description gives me the impression that a lot was coming out. So I'm thinking that maybe the coolant is coming out in a bubbling cauldron sort of way? And if there's a lot of bubbling, those gasses may be escaping fumes from the combustion chambers -- head gasket!!! Then, the large amount of coolant overflowing would be explained by it's being displaced by the gasses (via the leaking head gasket) accumulating somewhere in the engine's coolant passages.