your air box has trap doors in it that direct air and have foam tape that helps to seal the door’s when shut. the problem with yours is either the trap door doesn’t shut all the way due to a bad cable or acuator. OR the foam tape is missing/damaged/worn which is leading to a leak, which in turn means you are feeling air.
or it could be your blower motor resistor is bad if your truck has one
plus my car doesn’t blow air on me when i turn off the fan and i already have a supercharger on mine!