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I've rechecked the dryer and the vibration like sound happens when the regulating thermostat goes off. I noticed it happens as the voltages increases from 233 to 240 and the motor amps increases from 3.5 to 3.9. then stops when the regulating stat kicks in the the volts and amps return to 233 and 3.5. I can then switch from high heat to air and IMMEDIATELY the noise returns. Does that help?