Mortgage interest rates dropped again this week, setting new record-lows across the board. Analysts say we have bond investors to thank for the continuing declines. Investors are expecting the Fed to begin pumping more money into the economy to reinvigorate the now lukewarm recovery, so there's been a rush to buy up mass amounts of government- and mortgage-backed debt. This, in turn, has served to drive mortgage rates lower - now at their lowest point in more than a half-century.