Having pulled a driver's door from the yard to replace my dinged one, I have 1) sound proofed it, 2) replaced the window rollers, 3) put vacuum line around the door actuator rods; in other words, all the stuff that made my original door sound like a Lexus.
This one still sounds like a rattly old tin can when I close it and it is driving me nuts.
Do I have to check any internal welds or anything to stop it rattling? The outer skin near the hinge seems to flap a bit on closing as if it is not attached to the shell, but I will be damned if I can find anything out of place.
Should I just go get another door and consider this one a 'lemon'?

 

Remember that the inner door shell is for the most part unsupported. to prevent resonance of this peice it may require some weight added or some form or braceing to stop it. even in new vehicles this is rather common. Take the door panel off and tap around the inner door frame and look for your panels that shake. check your door handle for play on the outside and also check that the door panel isint rattleing aginst your new sound deadening.

 

sometimes.....the door skins can cause it to sound "tinny" as well. I just put a few dabs of panel bonding adhesive to the skin and to the impact bar in the door....

 

I found on my doors it was the interior armrest mount. I drilled out the rivets and replaced them with self tapping screws. They sound good now.