The fan or motor in the downdraft unit of my old Jenn-Air cooktop is making a loud noise whenever it runs. The unit worked perfectly fine until about two months ago when the noise began. The noise is so loud that it seems as if the fan is coming apart. However, the downdraft still draws plenty of air through it. Does anyone know what the problem might be and what part I need to replace to stop the noise? All help would be appreciated.