The 30-year, fixed-rate mortgage rate fell to 4.6% in the most recent Freddie Mac Primary Mortgage Market Survey, reaching a new low for 2011. That compares to a rate of 4.61% a week earlier and 4.84% last year. The 15-year, FRM followed suit, averaging 3.78%, down from 3.8% a week earlier and 4.21% last year. The 5-year, Treasury-indexed hybrid adjustable-rate mortgage  averaged 3.41%, down from a week earlier when it averaged 3.48% and down from 3.97% last year. Meanwhile, the 1-year, Treasury-indexed ARM averaged 3.11% in the most recent week, down from a week earlier when it averaged 3.15% “Fixed mortgage rates eased slightly for the sixth consecutive week amid reports of slower economic activity,” concluded Frank Nothaft, vice president and chief economist, Freddie Mac. Write to Kerri Panchuk.