Just how can an air filter make noise? I presume the sound your hearing comes from the idle air flow. (I guess no filter might allow noises to be heard).
If this is noticable you probably are also not idling at the right rpm. Normally the air volume is not enough to be noticable.
I would verify idle speed and would check the condition of the throttle plate (not airflow plate). Excessive carbon can keep the throttle partially open and/or change the volume of air that the idle motor (idle air valve) gives to establish the right idle speed.
Remember the air entering the motor is; all sources plus the idle motor equals 600rpm (or whatever your emissions sticker says). If there is unusually low amounts of air going through the carboned throttle then the airvalve compensates and adds more. This can become a whistle from volume. Just the opposite can also cause a whistle by having too much air flow and the valve closing to a point where the air flowing through the small hole whistles.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician