When I'm really close to the intake with the hood open it sounds like air like a "psssssssssss" type sound, when I turn off the car its a quick "pshhhh" sound, and when I touch the intake its vibrating with the engine. Is all this normal? My mechanic said the "psssss" type sound is normal because I have all straight piping, and that "pshhhh" sound is coming from the cynlinders rotating for a split second after the ignition turns off. Anyone else experiencing the same thing?

 

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Normal with most if not all aftermarket intakes with cone style filters