Does this happen when you run your a/c? I don't know if your car automatically runs the a/c when the defrost is selected, it might. Does the a/c work? Did you have the compressor replaced recently? The main pulley/dynamic balancer is designed to shear in the event that the a/c compressor seizes. This prevents the shock of the seized a/c from being transferred to the engine crankshaft. When the main pulley shears, it makes that loud squeeking noise. If this is the case, you have to replace the main pulley. You can confirm this by having someone run the car and the a/c while you watch the main plley from the left wheel well- KEEP YOUR FINGERS CLEAR!!! You will notice the pulley has an outer metal ring (where the belt rides) a middle rubber ring and the inner pulley. If you see the inner pulley turning at one speed ant the outer at another, that is your problem. You can also try to spray wd-40 on it to see if the noise goes away. Remember, don't get too close to those belts when the engine is running!!!!!!!