I assume your dealer has already done everything they can to eliminate noise from the door itself. Before turning attention elsewhere, however, make sure that the top and bottom outside corners of the door are making good seals when the door is closed. If not, the door may have to be cambered in at those corners with some sort a heavy retension strip screwed to the jam edge.
That said, there are a lot of things that can cause "door noise", besides the obvious door that is not tight fitting and lets in air. The most common is the awning arm right outside the door. Make sure it is tight when traveling, and that no air is getting through it. If so, the air needs to be deflected around. Also make sure that there are no stuctures inside the awining arm that are rubbing or rattling against each other.
Next, if there is a slide right behind the door, is that making a good seal when it's all the way in. How about the step well? Is that insulated well enough on the bottom side of the coach, or could you be getting noise from the road and wheel well? You can always glue foil backed foam panels to the underside and exterior sides of the stair well and paint them flat black.
How about the front right dash area. If you take off the windshield garnish between the deck of the dash and the windshield, can you see daylight in the area leading down to the road. If so, it needs sealed with expanding foam.
My last coach was a Fleetwood coach that had terrible door noise. I did all of the things I've mentioned here and was able to significantly reduce the noise.