Hey bro, try using Dynamat. no doubt you've heard of it, its a sound deadener usually used to stop vibration, reduce distortion and enhance your sound system atmosphere inside the car. i havent done it yet but i plan to soon coz i do get a few vibrations in my car, none really noted from having the window halfway down. i was going to do it when installing my sound system, but i (and many) would still recommend it for reducing vibrations inside the doors. you may need some help installing it if you plan to do it correctly, pulling the whole door apart including windows. but i warn u it can be expensive... look into it anyways. any good auto/car audio store will stock dynamat. hope this helps -ted