metal on metal vibration= loud clattering noise. metal on foam = no clattering. when you get a chance pop your hood and look between petween the outer sheet metal and the inner skeliton. you will see quarter size daps of foam from the factory......why? ....to prevent clattering vibration. btw you cant physically get dynamat in some places such as between a peices of sheet metal spotwelded together(like between the skeliton and sheet metal of a hatch or inner structure parts. like i said its a cheap quick fix, dynamat isnt a fixall either