The motor drive circuit or the motor is faulty. Also you have to check the carbon brush of the Motor .
If you wish to get some details; check the site linked here. Pull up older posts. http://electro-medical.blogspot.com/
If you can take the machine apart, perhaps replace the deck, if replacement isnt possible try coating it with a polyurathane in order to help reglue the fibers togeter. particle board WILL degrade over time with stress especially running.