When I get into my 83 300D Turbodiesel and start the car, I get a high pitched (but low volume) sound coming from the driver's side dash area.

Once all the doors unlock, the sound goes away. The same sound when I lock the driver's side door and goes away when all the doors lock.

My guess is that I am having a vacuum leak somewhere. My door actuators r fine and hold vacuum.

Some others have posted similar problem but no one seems to have encountered this issue.

What would cause this to occur ?