Interestingly enough, there is a fix for this! No really...
It appears that they even had the folks at DLR looked at this. The study was only on the A320, so I am going to assume it is specific to that ac.
From the study and images provided, it appears the slat configuration causes the noise. As the slat extends, airflow is directed to the space behind the slat, rather than the bottom of the wing...creating what they call as 'cavitation resonance'.
I find it similar to blowing across the top of a bottle.
The fix is to place a small tab on the bottom of the slat, or slots, to reduce the cavitation pressure and direct airflow back to the bottom of the wing, rather than up through the space...
(just so you know, they even tried messing with the AoA to solve this...but to no avail)
So, there you go....
Last edited by FlightPathOBN; 28th Aug 2012 at 20:52.