My spot bot has just started to do the same thing. Worked great last time we used it, and now the brushes don't turn and makes the same grinding noise. I tore mine down to inspect it and found it clean and a light amount of grease on the gears that drive it. The motor that power the brushes has voltage when the brush cycle comes on, and I discovered that if I try to "help" the motor out by turning the gear by hand, it tries to work. I've determined that the motor itself has worn itself out. I haven't had a chance to price the motor out, but I'd almost bet it won't be much cheaper than a new one.
James, January 2010
