That may have been the actual engine cooling fan you heard. I hear that a lot on mine when I stop during the first 10 minutes or so. Chrysler used to do that back in the 80s on their early computer controlled cars. The reason being is, in a cold morning, condensation builds up on the exterior of the radiator. You start driving and as the engine warms up the coolant, it cycles through the radiator which is full of cool coolant, keeping the engine cool without fan use. When you come to a stop, the warming up radiator will be burning off the condensation on it and on a humid morning could show up a faint steam/smoke/fog. People would think they had a leak or real problem, so they engineered a fix by causing the cooling fan to start when the car came to a stop for a few seconds until they thought it was warmed up enough to be dry.