Bought a used car and pads were replaced 20k miles ago. I've read on here of OEM pads typically wearing out around 30k miles. Recently, most likely due to hot weather, I've been getting squealing noise from rear left wheel (jacked up and free rolling). Since there should be another 10k miles (?) on the pads, I'm thinking maybe a dirt particle got stuck between pad and disc that's causing the noise? Is this possible or has the pad worn down to the indicator?