I have an Enviro EF5 evolution...stove has been great. Today out of the blue it started to make a little sound...then after a little while the noise got to be real loud. It only comes when you turn on the fan blower on the side of the stove to make the heat come out more. What would that be? Its to the point where its real loud. Like i said the stove only makes that sound when i turn the fan on. Any help would be appreciated.