i need some help i've a 94 wrx with a hks dump valve if i'm driving easy the d/v kinda whistles but if i drive hard it sounds like air is going back against the turbo,, its only like that with an air filter on. could it be the wrong dump valve on the car it was on it when i bought it

 

Is it a stutter kind of noise? If so its just your airbox sucking in more air, mine does it now ive got my DV sorted its kind of like a chatter effect.

 

yeah i was told by the lad that dyno'd my cr that it was the charge going back against the fins of the turbo and thought that the d/v wasnt the right one