I have a '13 sport 5mt and I have had this since day one. If I tap the throttle, it chirps. If I am cruising and give it a little gas, it hisses. Sounds almost exactly like when I had a small boost leak on my 03wrx. Like many of you, I have traced it back to the intake. My friend has the '12 sedan 5mt and his does not do this.
Also sort of related, I get an annoying metallic vibration sound from the exhaust whenever I rev or accelerate. I'm assuming it is relates to the heat shields. (Really noticeable when driving next to something: parked cars, buildings, Jersey wall)
Have any of you had that issue as well?