Several months ago I stopped by British Car Specialist in Stockton CA and David Nock showed my a BT7 they had just finished a complete restoration. When I opened and closed the doors, I was amazed at how smooth and solid they felt and sounded. David explained it was a combination of getting the perfect alignment of the door, latch and hinges and also a bit of sound deadener inside the door. I don't know how much or what they used, but the results were amazing. When I do my car over, I will add dynamat inside each door.