i just bought a 2000 witha 4.6l it has 140k miles on it and im hearing a tiny sound from the motor sounds like a heat shied rattle but think its from the motor were these engines famous for bottom ends blowing apart or what could it be

 

Not really, It could be a number of things. It could be a converter, heat shield, or even an exhaust leak from broken manifold studs.
Are you hearing it at an idle or while driving?