The secret is to use 3 each 1000 pf or .1mfd capacitors in a "triangle" configuration where there ua a "cap" from each terminal to the frame of the motor and a cap from terminal to terminal. Most motors require you to file off the coating on the motor frame so the frame will accept solder. It is necessary and required to connect a heavy "ground" wire from the motor frame to the negative connection on the main battery. Each cap will take the noise generated by the motor and "conduct" the noise to the frame and the frame will have noise on it from the motor brushes. Therefore the only way the noise can be elimated is by giving the noise to the battery. The battery will act as a "filter" and prevent noise from entering the rest of your electronics.
Just one more wire!