Washington Mutual has staked an early claim as the top producer in the ARM and jumbo markets for 2001, maintaining top rankings the company won by handy margins last year. According to a new Inside Mortgage Finance ranking and analysis, WaMu produced $9.42 billion of adjustable-rate mortgages during the first quarter of this year, more than double the volume of its next nearest competitor in the ARM market. The company reported that some 42.5 percent