Well, they use some kind of venting through the door handles...so it could be that; air hissing through the latch. I have noticed that with my A/C on, blowing at high speed...standing outside the car, when I put my hand on the latch to open the door, there is a cool breeze emanating from the front of the latch as soon as it depressed.

I have never noticed hissing with the windows down, but I'm in my 60's and my high pitch hearing isn't what it used to be.