This is a common complaint with newer doors as they are not sealed to allow for airflow. The thing you can do is remove the door and place it on a blanket. Then start removing the screws around the perimeter do separate the door. It is very important that you pay attention to how the door comes apart or getting it back together will not be nearly as much fun. The panels will separate so you can clean them then reassemble doors. It is most likely the inside of the outer panel that needs to be cleaned so only take it apart enough to clean what you need. If you get stuck, a look at the part breakdown may help.