Mortgage rates eased for a second week in a row on mixed economic news, but could be poised for a rebound after the European Central Bank announced a new round of bond purchases today that undermined prices of U.S. Treasurys, pushing up yields.Rates on 30-year fixed-rate mortgages averaged 3.55 percent with an average 0.7 point for the week ending Sept. 6, down from 3.59 percent last week and 4.12 percent a year ago, Freddie Mac said in releasing the results of its Primary Mortgage Market Survey. Rates on 30-year fixed-rate mortgages hit an all-time low in Freddie Mac records dating to 1971 of 3.49 percent during the week ending July 26.For 15-year fixed-rate mortgages, rates averaged 2.86 percent with an average 0.6 point, unchanged from last week but down from 3.33 percent a year ago. Ra...