Freddie Mac released its weekly update on national mortgage rates this morning, showing rates moving lower after being largely unchanged over the past month.

Thirty-year fixed-rate mortgages (FRM) declined five basis points to 3.51%, more than reversing last week's rise. Fifteen-year FRMs dropped one basis point to 2.76%. In both cases, rates are now at their lowest levels seen in more than a month.

Adjustable-mortgages are even cheaper. Among adjustable-rate mortgages, 5/1 ARMs fell three basis points this week to reach 2.61%, their lowest rate in years, while one-year ARMs dropped one basis point to 2.64%.

Commenting on the numbers, Freddie Mac Vice President and Chief Economist Frank Nothaft pointed out that lower rates don't necessarily make for cheaper housing. To the contrary, even with mortgage rates dropping, "the S&P/Case-Shiller national home price index rose 7.3 percent last year, reflecting the largest four-quarter growth since the third quarter of 2006."

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