When I first got fan it made a very irritating whine and I was not happy.  I do not run invertors due to the same sound.  Googled a camping website and a person said their fan whined and the person called Fantastic and was told to run the fan with reversed polsrity for a while.  I ran my fan reversed polarity for 10 min or so and when I hooked it up properly the whine was gone!,  I am very happy now!  I am guessing the bearings are sealed and motor pre lubed and running it backwards helps to spread the lubrication uniformally.  I have been listening to noisy 12v fans for a long time and my Endless Breeze fan is exactly what I dreamed of.  Now I have to see if it bothers my 12vLed tv when I go to my camper.