* Belt Wear and Tear: The most common culprit. An old, worn, cracked, or glazed belt loses its grip and will squeak, especially when cold or under load (like turning on the AC). The rubber becomes hard and loses its flexibility.
* Belt Tension: If the belt is too loose, it can slip and squeak. The tensioner pulley is responsible for maintaining the correct belt tension. If it's failing or improperly adjusted, the belt will be too loose.
* Dirty or Greasy Belt: Oil, grease, or other contaminants on the belt reduce friction and can cause it to slip and squeak. This could be from a leaking power steering pump, engine oil leak, or other fluid leak.
* Worn or Damaged Pulley: A pulley that's grooved, scored, or otherwise damaged will not provide a smooth surface for the belt to ride on, leading to slipping and squeaking. This is especially true for pulleys made of rubber or plastic.
* Water Pump Bearing: A failing water pump bearing can cause a squeak, particularly when the engine is cold. This is because the bearing may be stiff and the belt will be pulling at it harder.
* Alternator Bearing: A similar issue to a failing water pump bearing. A worn alternator bearing can also create a squeak, particularly when the alternator is under load.
How to troubleshoot:
1. Visual Inspection: Carefully examine the belt for cracks, glazing, or fraying. Look at all the pulleys for damage, grooves, or any signs of fluid leaks. Check the tensioner pulley to see if it moves freely.
2. Belt Tension Check: There are usually specifications for belt tension in your owner's manual or online repair manuals for your specific Silverado year and engine. You might need a special tool to properly measure tension, but you can often get a general idea by pressing on the belt midway between two pulleys. It shouldn't deflect excessively.
3. Listen Carefully: Try to pinpoint the source of the squeak. Does it change with engine RPM? Does it happen only when you use certain accessories (like the AC)? This can help narrow down the culprit.
4. Clean the Belt: If the belt is dirty, try cleaning it with a belt dressing specifically designed for serpentine belts (not WD-40, as this is a temporary fix that can attract more dirt and damage the belt further).
If you're not comfortable doing this yourself, take your Silverado to a mechanic. Ignoring a squeaking serpentine belt can lead to more serious problems, including belt failure, which can cause the engine to overheat or other components to fail.
