Hissing behind Center Console on Power Down

[iroessle]

Hello All,

Does anyone know why a hissing sound might be coming behind the center console of my 300D?

It doesn't happen while the car is on, only for about a second or two after I turn off the car. Sounds like air. Is this normal?

Notes:
The AC works great, the center vents kick in after the car is on and aren't engaged when the car is off.

Your efforts in helping me put this to rest is much appreciated.

-Ian