There are several reasons why a serpentine belt might become loose or worn. One reason is simply age and wear. Over time, the belt can stretch and become thinner, making it more likely to slip. Another reason is a misaligned belt. If the belt is not properly aligned with the pulleys, it can also cause a squealing noise. Finally, a faulty belt tensioner can also cause the belt to slip.
If you hear a squealing noise when first starting your car, it's important to have it checked out by a mechanic as soon as possible. A slipping belt can eventually cause damage to your engine.
