When I first start my care after it has sat for a while (couple hours or more) and begin picking up speed, there is a sound of a short burst of air being released.
This sound seems to be coming from the engine compartment or from the dash area. It does not continue after the car warms up, or it is so faint as not to be audible. It sounds like air under pressure and being released. The burst of air sound is very brief.