My 2001 Dakota, 4.7L V8 engine fan seems to make a loader noise when the engine is first started. As I rev the engine the fan seams to be pushing more are. Within minutes the fan air flow noise reduces and then doesn't reoccur until the next time I start the engine. It is not a squealing noise. It sounds like the fan pushes more air on initial start. Is this a problem or is this how the clutch type fans work?