The rattle you hear, is not really a rattle, but the vibrations of the motor.
I have heard many different fixes for this,, one is to move your Boost pickup line somewhere else,, (the noisest location to pickup your boost is by that bolt in the side of the head) Try drilling and tapping your intake horn,, or just add another 5'-10' worth of line coiled around itslef,, that will limit some noise,, or like Rock-n-Rammer siad, put a needle valve in line, and pinch it WAYY back.
Merrick