I had a motor do that but i got sent a replacement.. i found the old motor plug a few months ago as i needed a motor so i took it apart used the motor in something else and found no problems with the motor at all it ran fine but in the plug it ran crap.(halo1 plug) I think its going to be the way the motor is sitting in the plug casting. Maybe not the motor itself. Try undoing the 2 fixing allen key take the motor out clean up the contacts make sure its earthing right and you might find once fitted back together you'll be good to go. The way the motor fits into the plug and touches the back of the rca for the positive and the earth is the plug casting itself on to the motor very simple and effective but can have problems, relies on touch to get electic not soldering wires. Over time things move ie back of the rca or just plain built on a monday morning so things just isnt touching right could be the problem....

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