The best thing you can do is to add sound deading material to the inside of the doors. Go to a home base or home depot and get a roll of tar, usually 3 or 4 inches wide in a big roll, used for sealing around roofing vents etc., peel off the backing and apply it to the inside of the outside door panel, it will stick like crazy and will not fall off. It will add substantial mass and prevent the door skin from being a sounding board. You can also add it under the kick panels in the frount and the side panels in the back. Make sure you have deadened the trunk lid and have heat shield material inder the hood. Undercoating is good but also consider undercoating the inside of the car compleatly before installing the carpet, the bottom of the foot wells, also prevents rust. In order to make your car as quite as possible you have to dampen all the body panels fron the inside to prevent vibration, it's the sounding board effect that makes the big noise. Just tap on the outside of the door skin, it doesn't sound like a BMW, why? Because it vibrates and is not well dampened. The more places you can damp the quiter you car can be. Good luck Bob Ikola