Drive belt is worn out or loose or both. Replace the belt and check the alignment of the pulleys.
Alternator belt is probably loose and slipping. If you can turn the alternator by hand and the belt slips its too loose. Retension alternator belt
Turn the belt inside out. you need to get it under the power steering belt and to the other side of the pulley. You can use a crescent wrench to turn the pulley and get the belt under the other one. Turn the belt back right side out. loosen the alternator bolt and place the belt around the alternators pulley. Tighten the alternator bolt.
autozone.com has online manuals that give step by step how to You tighten the tensioner on the bracket holding the air conditioner to loosen that belt then you turn the hold that adjusts the tension on the alternator shifting it forward to loosen that belt. You will have to take the AC belt off first, then the alternator belt.
Remove the serpentine belt and check the belt and pulleys for damage. While the belt is off, turn the alternator by hand listening for the noise.
by putting you're seat belt on?....
Not enough belt tension.
Your belt going to the alternator is probably very loose and the motion of the turning alternator is continuing after you turn off the vehicle. Get the belt tightened right away.
Loosen tension regulating bolt for the alternator and the bolt attaching it the engines body, shift the alternator down and remove the belt. Install new one. Use regulating bolt to set proper tension. If you do not have tension meter, tighten until you can twist the belt only 3/4 of full turn.
you need to get a 3/8's drive ratchet w/ no socket, attach it to the belt tensioner and turn it to relieve the tension off of the belt. simultaneously pull the old belt off of the pulleys. to put the new belt on, follow the directions in reverse.
It sounds like the alternator belt is slipping with the high electrical load. Tighten or replace the alternator belt.
Replacing (or tightening) the main drive belt is very easy, you will need a 12mm socket wrench and a 14mm open end wrench. Loosen (do not remove) the two bolts above the alternator that are attached to the metal bracket that allow the alternator to slide (the alternator is attached to the topmost pulley that the drive belt touches, it is at the top front passenger side of the engine compartment). There is a 3rd bolt below the alternator, slightly difficult to see, loosen it using the 14mm wrench, it is often difficult to turn, I recommend penetrating oil and a breaker bar, you only need to turn it a little bit to allow the alternator to pivot. Once all three bolts are loose, you can easily rock the alternator back and forth (same procedure is used to tighten the drive belt). You want to push the alternator back to remove the belt. After installing a new belt (or to tighten an existing belt) you need to pull the alternator toward the front of the car as far as possible. The best way to do this is by putting a pry bar on top of and slightly behind the alternator and pushing up toward the windshield while using the engine as a pivot - this gives you plenty of leverage and allows you to pull the alternator forward. While you are prying, you can tighten the bolt that holds the alternator to the bracket using your left hand as you brace the pry bar with your right hand, to hold it all in place.