Quick update on this issue (c'mon, you know you've been waiting for it):
Finally had the car in for service, as I waited to get the window seal addressed in the same visit as the routine maint. Wasn't sure how this would be fixed as it seemed the rubber gasket / seal may have been damaged and might need replacing, but all they did was adjust the window in the track. Seems to have worked, as I have not been able to reproduce the telltale whistle and am enjoying a quiet cabin now.
Now my only issue is the noticeable "clunk" the window makes when first raising from a fully lowered position...