Bearings
Bearings will wear out on a wheelchair during normal use. Noise is the first thing that will alert you about a wheel bearing that is failing. Most prominently, a knocking noise, and on some occasions, a squeaky squealing moan is what would be the first indicator of such a problem. Initially, the sound would be heard only at certain speeds, but will become fairly regular and prominent as the condition of the bearings worsen.
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