I have a very similar complaint although the source of the whistling appears to be high up, above the window to the rear of the passenger side seat. I have tried to isolate without success, including the various taping techniques mentioned in other replies. I recall seeing a simliar posting somewhere where the source was found to be caused by the awning post, sort of a wind tunneling effect. I would be curious of others have found this to be the case and if so how they resolved the noise. Safe travels to all.