I had this same problem and lived with it for a year. It sounded as though it was coming from directly above the door, but on the outside. I figured it had to be the door awning. But when I checked, I could not find anything loose.
I had it in at the dealer (MHSRV) for some 1 year warranty work. When I described it, they immediately knew what it was and told me that is is very common on the Berks.
Apparently it is indeed a screw in the door awning. Unfortunately, I did not ask or see exactly where. But they did say that virtually all of them come loose and they tighten them during their checkout normally. Since they fixed it, it has been very quiet. I was relieved, and somewhat ticked that it took so long to figure out and fix.
Wish I could be more descriptive, but that's all they told me.
I also had the mud flap issue which was identified on the initial drive during PDI and corrected.