The noise!! It's not rattling nor rubbing, nothing externally off balance. It's all internal. The sound you get when the magnets and the rotors are not aligned. It's awful... worse on lower speeds. rotors designed wrong?!? Contrary to other reviews, it dosen't move air better than a 52 inch.... not even close. It vibrates too... this was installed in my finished basement and the flush mount made it so the rotor vibration was louder upstairs than it was in the basement. Moving to a seldom used bedroom and putting the old one back in.