Squeaky alternators are typically caused by a loose alternator belt, and all that is required to fix the problem is to tighten it. It is extremely important to tighten the belt because a loose alternator belt may cause the car to stall from not generating enough electricity to power the ignition system. If tightening the belt doesn't resolve the issue, you should replace the belt or use a belt stop squeal spray.
Open the hood and prop it up.
Loosen the alternator lock bolt with a ratchet. The lock bolt is located next to the alternator.
Tighten the tensioner bolt with a ratchet until you have approximately 1/2 inch of belt deflection. To measure belt deflection, place a ruler against the belt, perpendicularly, then push the belt down. If you are able to push the belt further than 1/2 inch, keep tightening the belt. If you aren't able to push the belt down 1/2 inch, loosen the belt.
Spray the alternator belt with a product called "belt dressing" that can be purchased from your local auto parts store if the issue is not resolved by adjusting the belt.
Replace the alternator belt with a new one if the noise is still present.
