Thanks for the comments secono. Maxi i'm not sure what 'gummy phledge' is so i'm affraid I can't answer. The windows sit inside a metal bracket, once these screws are lose the window rattles inside this bracket. It is a glass on metal rattle and happens when the window is open any amount on a bumpy road. When the window is shut the pressure pushing up holds the window still.
I figure this will only affect coupe and convertible drivers and is caused by people shutting the door by applying pressure to the glass and not the door itself. This applies pressure to these mountings and over time loosens them. Any one pushing my door shut with the glass will now get shouted at!!