1998 Ford Explorer Screeching Noises

When I start from a standing start with the lights on and heater/ac running the vehicle makes a loud screeching noise and it draws down on the battery/alternator indicator. If I turn the heater off the noise will sometimes go away.

If I turn the heater/ac on after the vehicle is moving at 15 mph or more I do not have the screeching sound. If I slow down below 15 or coast down a hill to maintain the speed limit it will start screeching too. I don't know if it's the battery or alternator.

Can you help, please?