Hello,
Just noticed this problem within the last week with my 2002 BMW M5.
When the windshield is foggy and I enable the climate control switch to remove the condensation and the AC is on there is water spurting from the air/AC vents behind the center console.
First I noticed a gurgling/sloshing sound but did not know where it was coming from. Then I turned around and saw water on the front side of the middle rear seats. Then the center hump in rear was wet along with the rear floor near the hump. Then I also noticed that there was water coming from the vents in the rear.
My solution at the time was to close the vents.
Not sure if this is normal.
Thanks,
GR