Thanks for the replies. I emailed hunterfan.mx but haven't gotten a reply yet.
I bought 4 Hunters in Mexico and they were all great, very quiet. I am now on my third new Hunter in the States and all of them hummed. No one seems to have an answer other than to switch to a DC fan, something which I will look into. I was thinking that perhaps the Mexican fans were made in Mexico and that that might be a clue as to the difference.