 The buzzing sound from the servo motor will drive you crazy.   The buzzing sound occurs when the interior air is trying to sync with the exterior air.   The sound is  louder than a cell phone vibrating and occurs every 5-10 seconds.  We purchased a 2015 Highlander in May 2015 and started hearing the buzzing a week after the purchase.  Replacing the servo motor requires taking apart the dash - an expensive proposition.  Due to the expense, Toyota is taking the position that the noise in "normal" and not under warranty.  Many online forums reflect this issue - search buzzing, noise, servo motor, etc.  Don't forget that the buzzing is loudest when the exterior and interior air are similar.  If you buy the Highlander in the Winter, the buzzing will drive you crazy come Spring.