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The Real Reason Belts Squeal, Chirp and Make Other Noise

If a newly installed serpentine belt  is making noise, it is a sign of a problem within the engine’s front end drive system. Serpentine belt noise is the equivalent to a “check engine” light that indicates something is wrong with the belt drive system.  But surprisingly, more often than not, the belt is not the culprit.

Squeals and Chirps: The Most Common Serpentine Belt Noises

There are two types of noise that a serpentine belt typically makes. One is the chirp, the other is the squeal. They each are the result of different issues within the front end drive system.

Serpentine Belt Chirp

The chirp makes a series of sharp, intermittent, “rhythmic” sounds. As the belt speed increases, the pitch and volume stay constant, hence why you hear a continued belt chirp when accelerating.

Six Reasons for the Chirp

• Pulley misalignment, the #1 cause of noise
• Improper installation
• Worn belt ribs
• Worn pulley bearings, which cause wobble or excessive free-rock
• Contamination from oil, power steering fluid, antifreeze or belt dressing
• A low quality belt was installed

Solutions for the Misalignment Chirp

• Check alignment of all pulleys, either with a straight edge or a laser alignment tool.
• Ensure all accessory pulleys and brackets are tightened snug to their mounting surfaces.
• Inspect and replace all accessories and pulleys that are difficult to rotate due to rough or seized bearings, or show excessive wobble or free-rock. Keep in mind that power steering pulleys and worn harmonic balancers can also cause misalignment.

Serpentine Belt Squeal

A squeal is high pitched, lasts several seconds, and may change in volume but not in pitch.

Top Three Reasons for the Squeal

1. Low belt tension either caused by low installation tension, a stretched belt, extreme belt wear, tension spring degradation or a belt that’s too long.
2. High accessory/idler pulley drag from seized bearings or accessory failure/lock-up.
3. Fluid contamination on the belt caused by exposure to belt dressing, oil, antifreeze or another chemical.

Solutions for the Tension Squeal

• Manual tensioned applications should be checked for proper tension (35 lbs. per rib) and then re-tensioned after 5 minutes of run-in (30 lbs. per rib). This allows the belt to seat in the pulleys.
• On vehicles with automatic belt tensioners, the tensioner pulley should turn freely without binding and the tensioner arm should move smoothly through its entire range of motion with adequate tension.
• Always check the tensioner bearing for noise and wear. Replace any tensioner where the bearing feels rough or the pulley has run-out.
• While the belt is removed, inspect all accessory pulleys and idlers to ensure free and smooth rotation. If there is binding or rough rotation due to a dry bearing, then the pulley and/or accessory should be replaced.
• If the belt is contaminated with motor oil, power steering fluid, antifreeze or any other petroleum-based lubricants, it will weaken and even cause the EPDM belt to swell and create noise. Any serpentine belt that has been oil soaked must be replaced.
• NEVER try to solve issues with belt dressing.

For more on belt noise or belt wear issues and quick tips to fix them, check out this video.

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