Research methods is a broad term. While methods of data collection and data analysis represent the core of research methods, you have to address a range of additional elements within the scope of your research.
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The most common reason disc brakes squeal is because the brake pads are worn out. Disc brake pads have a piece of metal built into them, which is called a wear indicator. As the brake pad material wears away the wear indicator starts making contact with the rotor, which produces a squealing sound. When you hear the sound it's time to have your brake pads checked and most likely replaced.