So, my fiance purchased this new off the floor before i met her (or else she wouldnt have bought it tho ill admit, im getting used to it. ). Had a motor issue which required a new motor after 90k miles.. Anyways, while driving on a normal road, i dropped the rear window and hear this whining noise. Checked the transmission fluid and it was a little low, nothing major. Topped it off with Mercon V... No effect. Where do i look next. It does not have a tow package. Do i check the transfer case, or rear differential?. Im torn.. Im thinking differential because the transfer case is more upfront to where the noise is. you cant hear it with front windows down. Only the rear sliding window or rear passenger's windows.