How do you stop a whistling noise that you hear when your Rav4 reaches 35 MPH?

as a former Toyota technician, i saw some of these "whistlers". Try changing the PCV valve with a new one from Toyota.

if that doesnt work (it probably wont) try removing the spars on the roof rack (if equipt). I see this from time to time and it will drive you crazy! also make sure the rear Windows are completely shut.