People with mobility issues that require them to use a wheelchair spend a big part of their day on those wheels. With a motorized chair, noise or vibration can quickly become an irritant and a distraction.
Manufacturers want to catch these issues before a unit leaves a factory, rather than having to deal with a return and an unhappy customer.
Unwanted noise or vibration affects customer satisfaction. It can also reveal part and assembly defects or identify a poor design.