Check the door seal - when its dark out, or in a wash bay or garage. Have someone run a very bright flashlight around the door frame opposite of you while closed. Do it both ways (inside and out) and look for the light leaking through. If you don't see anything then wind pressure could be changing the shape of the door and that will require someone to check the door while the vehicle is traveling.
2014 Fleetwood Discovery 40G -> '16 Yukon Denali
Mechanical and Electrical Engineer
"De Opresso Liber"