I have a Neptune 4000 dryer and lately when you first start it there is a strange noise. I know this sounds crazy but it is the closest thing I know to describe it-sounds like when a box fan is blowing and then wind blows against the fan how that sounds-well that is how this sounds. It drys fine and really doesn't make this noise the whole cycle just for the first few minutes. But then I don't really stay out there and listen-you know. What could this be? Also, I have metal duct, and I have checked it and it is clean even outside. To me this has always been a fairly noisy dryer but this sound isn't normal. Thanks for an ideas you have.