When I received my fan I noticed an intermittent whistle that increased or decreased depending on the speed setting.  I purchased this fan for use  in the evenings and night time in a small RV, and intermittent whistling is not compatible with either relaxing or sleeping,  I was prepared to return the fan to Amazon, or exchange it for a whistle-free one.  I listened to one of these fans that someone had posted on YouTube and I could hear theirs whistle in the same way mine did.