Some noise now that it will happen soon, despite a request for a postponement from New York regulators.What happens then?Jan. 30 (Bloomberg) -- Citigroup Inc., Merrill Lynch & Co., UBS AG and other banks may be forced to post up to $70 billion in writedowns should bond insurers lose their top credit ratings, according to Oppenheimer & Co. analyst Meredith Whitney.Citigroup, Merrill Lynch and UBS A