NEW YORK (CNNMoney.com) -- Mortgage rates fell for the 10th time in 11 weeks, though the drop was slight this week, according to a survey released Thursday.

The 30-year fixed-rate mortgage (FRM) averaged 6.30 percent for the week ending Oct. 5, down from 6.31 percent, according to Freddie Mac's (Charts) Primary Mortgage Market Survey. A year ago, the 30-year FRM averaged 5.98 percent.

The 15-year FRM averaged 5.98 percent this week, unchanged from last week. A year ago, it averaged 5.54 percent. This is the lowest 15-year FRM rates have been since March.

Rates for five-year adjustable-rate mortgages (ARMs) came in at 6.00 percent this week, unchanged from last week, the lowest they've been in six months. A year ago, they averaged 5.48 percent.

One-year ARMs averaged 5.46 percent, down from 5.47 percent last week. A year ago, the one-year ARM averaged 4.77 percent. The one-year ARM also reached a six-month low.

"Mortgage rates fell to a six-month low this past week, and, not surprisingly, home refinancing rose 18 percent last week, accounting for almost half of all mortgage applications," said Frank Nothaft, Freddie Mac vice president and chief economist, in a statement.

"This is due both to the recent decline in mortgage rates and to homeowners who are refinancing ARMs rather than waiting for them to reset in the future when rates may be higher."

"Even though rates have fallen recently, housing activity continues to slow while new construction wanes, leading Fed Chairman Bernanke to expect that the national economic rate of growth will lose up to one full percentage point in the last half of this year," he added.

Freddie Mac competes on the secondary market with Citigroup (Charts), Countrywide Financial (Charts) and Fannie Mae (Charts).