Dont forget that with any dump valve its position will remain the same,after the MAF.The sound you hear is through the intake system,an enclosed filter will mask the sound eg Dynatwist etc.My Green filter is an open one but sits inside the aluminium box with a cold air feed to the box.The air resonates through the box when the valve dumps and as stated before it is loud.When I put the original filter housing on it was barely audible!It must be down to the installation of my intake/box/filter arrangement.