My 2011 does the same thing,had it at dealer twice and they couldnt fix it. So i looked at it myself (im a kia technician) and found when the recirculation door is not sealing properly alowing air to pass and whistle. If you remove your glove box and look straight back you can see a mesh cover that is removable and behind that is the recurculation door. When that door is closed (white showing) turn on blower motor with all doors and windows closed and it will whistle. Use a small screwdriver and lightly push down on door and whistle stops. If you turn blower on and set it to vent and push the recurculation button the door moves up blocking fresh air intake and whistle stops. Push recurculation button again and door moves down and just as it is fully closed it will move up just a little causing noise. Since the dealer was no help i got some thin foam tape(foam on one side, sticky on other) and stuck it on hvac box where the recurculation door sits. No more anoying whistle noise. Hope this helps you as it helped me.