The average U.S. rate on a 30-year fixed mortgage fell this week to a record low for the seventh time in eight weeks. Cheap mortgages have helped drive a modest recovery in the weak housing market this year. Mortgage buyer Freddie Mac says the average on the 30-year loan dropped to 3.66%. That's down from 3.71% last week and the lowest since long-term mortgages began in the 1950s. The average rate on the 15-year mortgage, a popular refinancing option, declined to 2.95%. That's down from 2.98% last week and just above the record 2.94% reached two weeks ago. The rate on the 30-year loan has been below 4% since December.