Q: Changed alternator and battery now car makes a noise when you start it up

This is a common sign of a loose or worn belt. This may have happened when you replaced the alternator potentially tightening the belt too tight. When this happens as you press the gas pedal and the belt goes from a relatively low speed (at idle or when first starting the car, no speed at all) to a much higher speed as the engine accelerates, this can cause the belts to squeak. This can happen when they stretch due to the fact that the pulleys on your car’s engine are turning faster than what the belt can keep up with when it is not tight against the pulley. This can also happen in extremely cold weather conditions due to the fact that the rubber belts become slightly brittle and less pliable in cold weather. I would recommend having an expert from YourMechanic come to your location to diagnose and tighten or replace your belts.