When I swapped out the factory air box for the ST200, I started hearing the GFB Diverter Valve, (albeit NOT all of the time, and it is muted when I do hear it), whereas with the factory unit, it was dead silent (this is with BOTH using the thick factory Motorcraft paper filter, BTW), if that is any indication.
This is with all other intake piping pure factory stock.
But still far far quieter than any of the noises a 2J Racing, ITG, or any of the other 'open element' systems would produce.