I have a 2002 XLT 5.4 4WD. Lately, when the rpm's hit 2000 (almost exactly) a loud, tinny rattle like sound comes from the passenger side of the engine. Any idea what this could be? No sign of sound at idle or under 2000. Doesn't sound like an exhaust leak... Any help would be greatly appreciated!

 

Check the heat sheilds on your cats.