I keep reading of 'wizzing fans' *This may seem trivial but it isn't*. Look at the fans, make sure they are spotlessly clean, I had to find a sharp object to scrape around and inside my fan, it is difficult to get by the blades but it must be done, they do not wizz for nothing. All the snags went away after I cleaned them.....and added some memory strips! I never hear a fan now.