The whistle may be caused by the window latch. Spray silicone in the window tracks, close the window with a little slam, and make sure the latch engages the groove completely. If the window isn't completely closed and you flip the latch it pushes the window open slightly causing the whistle. This is a common problem, takes a while for that fuzzy stuff in the window track to break in.
We found several loose screws laying around in our coach too!
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