My 1999 528i developed an annoying, faint rattle near the driver's A-pillar when touring on holiday recently. I had been on some unsealed roads so the car has become quite dusty. When I washed the car, I found that the rubber seal on the door that meets the A-pillar (at or just below the level of the instruments) was dusty and had obviously been fretting on the A-pillar. Cleaning it fixed the problem. This seal isn't felted like the seals around the top of the door frame.
Just thought I'd share this......cheers