Anybody encountered this problem?

I've repaired, painted, re-built, re-hinged and rehung  both front doors.

>From one door, I'm getting a high-pitched whistle. This is coming from the 
window scrapers. What's happening is that at speed or when there's a strong 
wind, air pressure is building up inside the door cavity and this is blowing 
out between the scrapers and the glass. Opening the vent in the bottom of 
the panel reduces the problem but doesn't remove it.  If I remove the door 
panel and the polythene foil, the problem disappears. If I block off all the 
ventilation holes, the problem disappears.

The external scraper is new, the interior scraper is probably original but 
in good order. Neither scraper is particularly tight or loose. Both are 
causing the whistle.

The other door is fine and I've never come across this on any other Type 2.

???

Any suggestions would be appreciated. This is one noise, of the various 
clunks, rattles and squeaks, that I can't live with.

>From: David Tonks. Westfalia 1972 (UK)