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I checked one in a insulated room with my radioshack meter. It dropped from the rated 70db to 60-62db. Outside the room sounded like an ac unit running maybe a large fan...

Reminds me of something I heard about the (very)large stationary engines, they pump the oil out of the engine(hundreds of gallons) they filter, test, and restore it with additives, then pump it back into the engine.