Why are there 2 metal blocks attached to the top of the exhaust pipe of my 2007 5.4 F150? They aren't associated with any mounting brackets and are about 3/4 inch high and about 2 inches long mounted about an inch apart back towards the bed of the truck before the muffler. If it were a drive shaft it would look like balance weights were attached. Are they some sort of anode to prevent rust?

 

I haven't seen them, but it sounds like it may be a NVH (Noise, Vibration and Harmonics) damper. Ford might have found out that the exhaust pipe likes to vibrate at a certain speed (probably right at some common speed, like freeway cruising) so they tacked a couple of slugs of metal onto the pipe to change the vibration characteristics.

 

Sounds plausible. By doing this you would change the natural frequency there for moving the rattling up or down from the point of interest.