See that the check strap is firmly attached. Might have worked loose, causing the rattle. Door panels are a snap, just be sure to work slowly and have all retention devices removed before trying to lift on the panel (don't forget the the window trim piece).
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.