This was a regular occurance in my '03 Liberty and also in by current Nissan Frontier Crew Cab. Always put the front window down more than the rear window. Also if you put all of them down all the way, it will be breezy, but fairly quiet. Hope your wife doesn't have long hair!
This is just a fluke with the high cabin and air waves rippling down the sides of the vehicle. You could probably get rich quickly if you could engineer some kind of add-on for the 'A' pillar that doesn't restrict driver view that would smooth the turbulance. When you have a chance to drive with the front window all the way down, put your hand out the front window and feel how much wind is deflected back against the vehicle by the side mirrors. If they were smaller, that would reduce the warble somewhat. If the Nitro is yours, you will get used to it. If it's your wifes, she will tell you about it everytime you get in it with her.
You might want to lock out that rear window switch from the little ones.