According to others in another forum who have the same saw, it doesn't have anything to do with the belt. Supposedly, "some" motors do this and some don't. I just depends on which one you got. What is actually happening is that (when the saw is shutting down) the centrifugal switch contacts close, the capacitor will dump its charge across the windings which cause (sometimes violet) shudder. The proposed solution is to add a "bleeder resistor" to bleed off the capacitor charge before shutting off the motor. Regardless, I feel like it is a major flaw in the design of the motor.
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