You might also find a pair of 103 ceramic capacitors, soldered between the terminals and the metal body of the motor. They do exactly the same, providing a path for RF energy coupled from the rotor to the case to return, so that you reduce EMI off the motor. On universal motors you commonly find this in a small block, with mains on 2 terminals before the motor, and a third connection to the frame. They normally use the 2 field coils to do double duty as RF chokes as well, one each side of the commutator, so the electrical noise of the brushes is confined to the motor itself and does not escape down the power cord.