I think the hole the previous posts were referring to is on the top of the mirror arm where it connects to the door. I occasionally hear the whistle, but it hasn't bothered me enough to cover it.
I took our Seneca in to the local Freightliner Service Center for its first annual service last week and asked them about the service bulletin for the transmission noise. They said that it didn't apply to my chassis. They did perform the parking brake recall, though.
Ty & Deb Montag
2015 Jayco Seneca 36FK
2014 Honda CR-V toad