Prices on agency mortgage-backed securities dropped Thursday as fears of faster pay-downs on these bonds ricocheted through the market. The decline was particularly sharp for securities with lower interest rates. The price of a Fannie Mae 30-year bond with a 4% coupon, for example, fell to 102 18/32 from 103 9/32 at open on Tuesday, a loss of $7,1875.50 per $1 million of investment. Bonds with 5% coupons fell to 105 19/32 from 106 1/32, according to Tradeweb data; that would be a $4,375 loss on a $1 million investment.