I have seen several Flies recent in my house, not sure where they are coming from , I heard something in my daughter wall last month? not sure if it something in the wall that has died or if it's something in the attic , to scared to go up there to check ,what should I do (HELP) .

Hire an exterminator. Yes, probably a dead animal in the wall or attic. You can buy 'bombs' at hardware stores (spray can with clamp that makes it stay open while you run away) and set it off in the attic, but you still have to go back and put the dead animal in a plastic bag and dispose of it.