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There are a few things than can cause grinding. It could be the bearings on the rollers have started to wear and or the motor brushes have worn down and are starting to grind on the motor armature. You could try spraying some WD40 into the roller bearings to see if that helps. Do you get any error message when the machine stops? This company in the UK might be able to help with repair if needed. http://www.treadmilldoctor.co.uk/