Do it yourself

We have a Sear's electric extra capacity cloths dryer, bought in August of 1999, so it is fairly new. It has a neat feature where it will "whissle" when the lint filter is full. Now it whissels all the time even with an empty lint filter. The hose to the outside does not appear to be glogged. The outside flaps are clean and blow dryer air hardily when the dryer is in operation. Does anyone know how to get at this whissel to remove it, or fix the problem? Thanks kindly, Dave