Whats that "depressurization" noise in A319/20/21

[Too Low Terrain]

Hi Folks
Anybody out there who can explain the exact source of that
"depressurization noise" which comes on during descent somewhere
below FL80 or so ?

It sounds like coming from somewhere behind the circuitbreaker panel
and its only in (the last part of) descent, however I cannot really
locate it nor explain the reason for it.

It sounds like....well.......a continuous.......err......"psshhhhhhhhhhhhhhh....."

Any explanation welcome !

[Aztec Kid]

Most likely, what you are hearing are the keel beam drains. I believe they open at 2.0 PSID.
The Kid

[E cam]

I think the noise comes from the floor grill, just in front of the flight deck door. It is more obvious in the 321 than the 320. More keel beam drains?

[walkertonio]

Maybe it is your bottle of water which doesn't support the change in differential pressure ?

[SFCC]

Aztec Kid is right........just take a look at the delta P indication next time it starts. It will be 1.9 or 2.0 psi guaranteed.