I noticed the same Problem also. I have to drive over 300 miles to go to a Hospital at times, I have a spinal cord injury, and I found that by putting the rear window behind the driver seat down a few notches helps the air circualte without all the noise that you get with the front driver side window down. When we drive those 300 miles the speed limit is 110 kilometers, or higher when I drive haha, and there all highway miles, plus I'm a smoker and it helps to get the smoke out of the Rav4 also. My wife is a smoker also so don't go jumping all over me now lol.
But it is the aerodynamics as previously mentioned, that causes all the noise when the front window or windows are down.
I hope this helps.
Take Care and Happy Rav'n
OzzyO