Investors clamoring for the safety of long-term government bonds, sent mortgage rates lower for the second straight week, according to Bankrate.com. The average rate on a 30-year mortgage fell to 6.74 percent, down from 6.76 percent last week, but up from the 6.32 percent rate seen in mid-May. Rates on a 15-year fixed mortgage stood at 6.4 percent, down from 6.45 percent last week. Rates on a 5/1 adjustable rate mortgage stood at 6.47 percent.