Recently I have noticed that a second or two after starting my 1999 3.8 I hear what sounds like the engine fan but it is not. It goes away after a minute or so. I do not hear it at all when the engine is not at idle. If i get to a traffic light and sit for 30 seconds or so when the engine is fully warmed up it will start again, but stops the instant I press the gas peddle down at all. When I listen closely from inside the car, it sounds like it is coming from the area of the middle of the firewall. Outside the car I cannot hear it over the exhaust and other engine sounds. Any thoughts of what it might be? I cannot seem to localize it and don't want something to suddenly go bad on the road.