Cold Start Noise
WARNING: This page is about a different car, the 2006 Mercury Mariner and 2006 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.
Cold start noise is the air-borne noise generated by pump cavitation when hydraulic fluid does not flow freely through the suction hose from the reservoir to pump. Zip is primarily a cold weather start-up phenomenon. Some noise during an extremely cold start (-12.2°C [-10°F]) is normal and should improve as the steering system warms up (usually within 60 seconds).