i have the SC cold air intake and K&N filter. the noise was there with the stock air box and the now with the CAI and K&N. it does sound like a whistle coming from air getting sucked in
I'm not sure whats the source is but it is related to the throttle. it starts low and gets louder as a step more and more on the gas but when i punch the pedal all the way down the noise is gone.
I ruled out the air box, TB, pulleys and belts; all of these parts were changed.

95 SE MTX DH UIM, 65mm TB, SC CAI, Quaife, Centerforce, Fidanza, UR Pulley, F/R Strut Braces, Cross Drilled Rotors, S.S. Brake Hoses, 18" Enkei RS5, SVT Engine Mounts+Inserts, MSDS & y-pipe, Trubendz resonated exhaust & MagnaFlow cat