Symptoms
- Squeal appears mainly in rain, fog, or high humidity
- Brakes are quiet in dry weather
- Noise may lessen after a few minutes of driving in the rain
Likely causes
- CommonLight surface rust forming quickly on rotors in wet weatherBare rotor metal rusts fast in moisture, and the pad scraping it off can squeak.
- CommonMoisture temporarily changing the friction characteristics between pad and rotorSome pad compounds are more prone to noise when wet.
- PossiblePads nearing the end of their life, more noticeable when wetWorn pads can be quieter when dry but squeal more readily once wet.
What to do
- Note whether the squeal is specific to wet or humid conditions and quiet otherwise.
- Check if the noise lessens after driving a few minutes in the rain, as pads clear the moisture off the rotor.
- Check pad thickness if you haven't recently, since worn pads can make this more noticeable.
- Consider this normal if it's isolated to wet weather and pads are in good condition.
- Have a mechanic check pad thickness and rotor condition if you want confirmation or if noise seems to be getting worse over time.
When to call a pro
No professional needed if squeal is isolated to wet weather and pads test fine; see a mechanic if it's paired with thin pads or the noise carries over into dry conditions too.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.